The 2013–14 season was Chelsea Football Club's 100th competitive season, 25th consecutive season in the top flight of English football, 22nd consecutive season in the Premier League and 108th year in existence as a football club. In addition to the domestic league, Chelsea participated in the UEFA Champions League this season, having qualified directly for the group stage by virtue of finishing third in the 2012–13 Premier League. It ultimately reached the semi-finals, losing there to Atlético Madrid. Chelsea came third in the Premier League for a second successive season, thus again qualifying for the Champions League group stage. Chelsea ended their 2013–14 campaign without a trophy, a first since the 2010–11 season. Their league performance, however, was the best since the 2009–10 season, with the team amassing 82 points.

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Month-by-month review

June

On 3 June, Chelsea announced that former manager José Mourinho had been appointed as the new manager for the 2013–14 season. He signed a four-year contract with the Blues, up to the end of the 2016–17 season. He was re-united with former squad members John Terry, Frank Lampard, Ashley Cole, John Obi Mikel, Petr Čech, Henrique Hilário and Michael Essien whom he brought back from his loan spell at Real Madrid. Mourinho also brought three coaching staff members with him to Stamford Bridge in Rui Faria, Silvino Louro—both of whom had worked at Chelsea under Mourinho's previous tenure—and José Morais. Mourinho was officially announced to the media on 10 June and took charge of the team on 1 July for the pre-season. One of Mourinho's first games was against Barcelona rival Pep Guardiola, as he managed 2012–13 UEFA Champions League winners Bayern Munich in the 2013 UEFA Super Cup at the Eden Arena in Prague. In Mourinho's first official interview back, he referred to himself as "The Happy One" in regards to his appointment as the new Chelsea manager, having called himself "The Special One" during his first tenure.

On 13 June, Chelsea and Bayer Leverkusen reached an agreement for the transfer of André Schürrle, subject to the completion of legal documentation and related matters, including personal terms and passing a medical.

Following the release of the 2013–14 Premier League fixtures, Mourinho's first match in charge since his return was at home against Hull City. Chelsea then faced a trip to Old Trafford for David Moyes' first home game as Manchester United manager. The Blues will finish their campaign away to Cardiff City. During his first spell in charge at Chelsea, Mourinho was unbeaten in 60 league home games.

On 21 June, the club announced a contract extension with Adidas that will see them supply the club kits until 2023. This deal means that Chelsea, along with Arsenal, hold the record for the biggest shirt deal in the history of the Barclays Premier League, valued at £300 million.

Chelsea completed the signing of André Schürrle for a fee of around £18.75 million. Schürrle became Mourinho's first signing since returning to the club, signing a five-year deal. He is the first player to wear the number 14 shirt since Claudio Pizarro in 2007–08."Schurrle signing completed" . Chelsea F.C. 25 June 2013. Retrieved 22 January 2014."Chelsea confirm deal to sign André Schürrle from Bayer Leverkusen". The Guardian. 13 June 2013. Retrieved 21 January 2014.

Marko Marin left Chelsea to go on loan at Sevilla for the duration of the season while Todd Kane and George Saville also went on season long and half-season loans to Blackburn Rovers and Brentford, respectively. Meanwhile, goalkeeper Thibaut Courtois will remain on loan at Atlético Madrid for at least another season.

A number of players were released by the club; Yossi Benayoun, Florent Malouda; who joined Trabzonspor in Turkey; Ross Turnbull, who signed for Doncaster Rovers; and several youth prospects that failed to live up to expectation. Paulo Ferreira retired from football after several years at the club and Jeffrey Bruma was sold to PSV for £2.5 million.

July Chelsea signed midfielder Marco van Ginkel from Dutch club Vitesse for an undisclosed fee, but a reported £8 million deal. The 20-year-old signed on a five-year deal and was Chelsea's second signing of the summer. Van Ginkel won the 2012 Dutch Football Talent of the Year.

Chelsea also announced the signing of former Fulham goalkeeper Mark Schwarzer, on a free transfer. After having two bids rejected for Norwich City goalkeeper John Ruddy, Mourinho decided to sign Mark Schwarzer as back up for Petr Čech. Oriol Romeu left Chelsea to go on loan at Valencia for the entirety of the season, while West Bromwich Albion youngster Isaiah Brown was signed for around £250,000. Mourinho won his first game back as Chelsea boss after overseeing a 1–0 friendly victory over the Singha All-Stars on 17 July in Chelsea's first leg of their Asian tour in Bangkok. A few days later, on 21 July, Chelsea won the second leg of their Asian tour with a 4–1 victory over a Malaysian XI in Shah Alam. On 23 July, Chelsea announced the signing of Cristián Cuevas from Chilean club O'Higgins.

Chelsea rounded off their Asian tour with an 8–1 demolition of the BNI Indonesia All-Stars in Jakarta on 25 July.

A number of young players were sent on loan to gain first-team experience; Patrick van Aanholt and Gaël Kakuta were both sent on loan to Vitesse for another season, Matej Delač was sent on a season-long loan to Vojvodina in Serbia, whilst Sam Walker and Daniel Pappoe were both loaned to Colchester United for the first half of the season. Additionally, Patrick Bamford, Billy Clifford and Milan Lalkovič were sent on half-season loans to Milton Keynes Dons, Yeovil and Walsall respectively, whilst Eden Hazard's younger brother Thorgan also saw his loan with Zulte-Waregem in Belgium renewed for the season.

August On 1 August, Chelsea announced that senior reserve goalkeeper Henrique Hilário had signed a new one-year deal after his contract had expired in June."New deal for Hilario" . Chelsea F.C. 1 August 2013. Retrieved 22 January 2014. Another youngster was signed, teenage Croatian striker Stipe Perica. Eighteen-year-old defender Nathan Aké signed a new five-year contract with Chelsea, he made six appearances for the Blues last season.

Chelsea recorded a comfortable 2–0 victory over Inter Milan in Round 1 of prestige exhibition tournament the International Champions Cup on 1 August in Indianapolis. Chelsea registered another win in their Round 2 fixture three days later on 4 August, once again a comfortable 2–0 victory, this time over Internazionale's cross-town rivals Milan in New York City. On 7 August, Chelsea lost their perfect pre-season record after they were defeated in the International Champions Cup final by Real Madrid in Miami, losing 3–1. Chelsea won their final game of pre-season in a 2–1 victory over Roma in Washington, D.C., on 10 August. This marked the end of a largely successful pre-season for Chelsea, registering wins over Italian top flight opposition in Inter, Milan and Roma, while comfortably defeating three Asian sides.

Yet again, more youngsters were sent on loan and in keeping with Chelsea's special relationship with Vitesse, newly signed Chilean youngster Cristián Cuevas and Lucas Piazon were sent on loan to the Dutch side while Jhon Pírez will spend another season out on loan at third division Spanish outfit Leganés. Promising young full-back Wallace was sent on loan to Inter Milan and newly signed striker Stipe Perica joined NAC Breda.

On 18 August, Mourinho won his "second" first competitive game in charge of Chelsea with a 2–0 victory over Hull City. Despite Frank Lampard's early penalty miss, Oscar gave Chelsea the lead, poking the ball under the onrushing Allan McGregor after a sumptuous passing move. A superb 35-yard free kick from Lampard sealed the win before the half-hour. The victory meant that Mourinho's Chelsea were unbeaten at Stamford Bridge in 61 league games. Chelsea continued their strong home form under Mourinho with a narrow 2–1 win over Aston Villa on 21 August. An own goal by Antonio Luna opened the scoring after Brad Guzan's save from an Eden Hazard shot rebounded off of him and into the net. Villa later equalised through a quickfire shot from Christian Benteke inside Petr Čech's near post, but after 73 minutes, Branislav Ivanović connected with Lampard's free kick to head home the winner. On 28 August, it was confirmed that Chelsea had signed Willian for £30 million from Anzhi Makhachkala. It was reported that Roman Abramovich used his Russian connections and called the Anzhi owner to convince him to join, even though he had already completed a medical for Tottenham Hotspur.

In their final game before their UEFA Super Cup clash with Bayern Munich, Chelsea were held by Manchester United to a dour 0–0 draw at Old Trafford on 26 August. Just before Chelsea were drawn in the 2013–14 UEFA Champions League group stage, they announced the signing of Samuel Eto'o from Anzhi in a deal believed to be around £2 million. Chelsea were drawn in Group E alongside Schalke 04, Basel and Steaua București. Last season, Chelsea defeated Steaua and Basel on their way to the 2012–13 UEFA Europa League title.

On 30 August, Chelsea were beaten in the UEFA Super Cup by Bayern Munich on penalties at the Eden Arena in Prague. The match was a tense encounter largely dominated by Bayern, but Chelsea were dangerous on the break, opening the scoring through a fantastic strike from Fernando Torres, who was set up by André Schürrle, who had received the ball from Eden Hazard following a mazy run. Bayern equalised through a sweetly struck shot by Franck Ribéry inside Petr Čech's near post. With five minutes left, Ramires was sent off for a second bookable offence leaving Chelsea to face extra-time with ten men. Early in the first half of extra-time, Hazard put Chelsea ahead after beating two Bayern defenders and wrong-footing Manuel Neuer. Chelsea managed to hold on until the final five seconds after spending much of extra-time camped in their own 18-yard box, but Javi Martínez broke their hearts putting the ball past Čech after a deflection carried it into his path. During the penalty shoot-out, all the players on both sides scored their penalties up until Chelsea's final penalty taker, Romelu Lukaku, hit a tame penalty that was saved by Neuer, thus sealing the win for Bayern.

September Chelsea announced the signing of Porto winger Christian Atsu for a reported £3.5 million. The 21-year-old was sent to Chelsea's partner club Vitesse, who have been sent many young Chelsea players for development in recent years, on a season-long loan. On the final day of the transfer window, Victor Moses and Romelu Lukaku joined Merseyside clubs Liverpool and Everton, respectively, on season-long loans whilst Ulises Dávila was sent to Córdoba in Spain. Later in the month, young English players Nathaniel Chalobah and Josh McEachran were sent on loan to Nottingham Forest and Watford, respectively, until the turn of the year.

On 14 September, Mourinho suffered the first defeat of his "second coming" as Chelsea were defeated 1–0 by Everton through a Steven Naismith header in first-half stoppage time after an impressive defensive display by the Merseyside club at Goodison Park. Four days later, Chelsea suffered a shock defeat by Basel in their opening group game in the Champions League at Stamford Bridge. Chelsea opened the scoring just before the interval through a tidy finish by Oscar from eight yards out, though two quickfire goals for Basel in the last 15 minutes from Mohamed Salah and Marco Streller condemned Chelsea to their first-ever loss in an opening group game of the Champions League.