is a Japanese-Australian tennis player. He represents Japan in competitions, though he played for Australia from 2010 to 2015, and from 2017 to 2025.

Early life Santillan was born in Tokyo to a Japanese mother and a South African father. He lived the first 8 years of his life in Japan before his family relocated to the Gold Coast, Australia and became citizens. He played much of his junior tennis at the Gold Coast before moving to Brisbane to join the national academy program at the Queensland Tennis Centre.

Junior career On the junior tour, Santillan has a career-high ITF junior ranking of 7 achieved in September 2015. Santillan's major highlights on the junior tour included a semi-final at the 2015 Australian Open and doubles finals at the 2014 French Open and the 2015 Wimbledon Championships.

In March 2015, Santillan opted to play under the Japanese flag instead due to a fractious relationship with Tennis Australia. He returned to playing under the Australian flag in 2017, before switching back to Japan in 2025.

Junior Grand Slam finals Doubles ResultYearChampionshipSurfacePartnerOpponentScoreLoss 2014 French Open Clay Lucas Miedler Benjamin Bonzi Quentin Halys 3–6, 3–6Loss 2015 Wimbledon Grass Reilly Opelka Lý Hoàng Nam Sumit Nagal 6–7(4–7), 4–6

Professional career Santillan has a career-high ATP singles ranking of 160 achieved on 24 July 2017. He also has a career-high ATP doubles ranking of 265 achieved on 17 July 2017. Santillan has won 6 ITF Futures singles titles and 1 ITF Futures doubles title.

Santillan made his ATP main draw debut at the 2016 Generali Open Kitzbühel, receiving singles and doubles main draw wildcards.

Santillan lost in the first round of the 2022 Australian Open – Men's singles qualifying.

Challenger and Futures/World Tennis Tour finals

Singles: 18 (12–6) Legend (singles)ATP Challenger Tour (1–0)ITF Futures/World Tennis Tour (11–6)Titles by surfaceHard (11–5)Clay (1–1)Grass (0–0)Carpet (0–0)

ResultW–LDateTournamentTierSurfaceOpponentScoreWin1–0Thailand F1, BangkokFuturesHard Kento Takeuchi6–3, 6–2Loss1–1Thailand F2, BangkokFuturesHard Andre Dome4–6, 7–6(9–7), 1–6Win2–1Spain F7, MadridFuturesHard Steven Diez6–4, 7–6(7–5)Loss2–2Spain F11, MostolesFuturesHard Antoine Escoffier4–6, 7–6(7–5), 3–6Win3–2China F7, WuhanFuturesHard Chung Yun-seong6–1, 6–4Win4–2China F8, LuanFuturesHard Finn Tearney6–3, 1–6, 6–4Win5–2Spain F18, Palma del RíoFuturesHard Rémi Boutillier7–5, 6–3Win6–2Spain F39, Cuevas del AlmanzoraFuturesHard Roberto Ortega Olmedo6–1, 6–1Win7–2Winnetka, USAChallengerHard Ramkumar Ramanathan7–6(7–1), 6–2Loss7–3M25 Canberra, AustraliaWorld Tennis TourHard Dane Sweeny 3–6, 6–4, 5–7Loss7–4M25 Monastir, TunisiaWorld Tennis TourHard Yasutaka Uchiyama6–7(3–7), 7–6(7–5), 3–6Win8–4M25 Monastir, TunisiaWorld Tennis TourHard Li Zhe2–6, 7–6(7–3), 6–2Loss8–5M25 Mungia, SpainWorld Tennis TourClay Inaki Montes-De La Torre3–6, 5–7Loss8–6M25 Portimão, PortugalWorld Tennis TourHard Gonçalo Oliveira6–7(2–7), 4–6Win9–6M15 Antalya, TurkeyWorld Tennis TourClay Stefan Popovic6–1, 6–1Win10–6M15 Ma'anshan, ChinaWorld Tennis TourHard Kasidit Samrej3–6, 6–3, 7–6(7–5)Win11–6M15 Yinchuan, ChinaWorld Tennis TourHard Tianhui Zhang7–5, 6–3Win12–6M25 Huzhou, ChinaWorld Tennis TourHard Chase Ferguson6–4, 6–1

Doubles: 17 (9–8) Legend (doubles)ATP Challenger Tour (2–5)ITF Futures/World Tennis Tour (7–3)Titles by surfaceHard (8–5)Clay (1–3)Grass (0–0)Carpet (0–0)

ResultW–LDateTournamentTierSurfacePartnerOpponentsScoreLoss0–1Spain F6, TarragonaFuturesClay Gonçalo Oliveira Marc López Jaume Munar7–6(7–4), 3–6, [7–10]Loss0–2Spain F8, MadridFuturesHard Carlos Gómez-Herrera Carlos Boluda-Purkiss Alex de Minaur4–6, 4–6Win1–2China F7, WuhanFuturesHard Harry Bourchier He Yecong Wang Aoxiong4–6, 6–2, [10–7]Loss1–3Segovia, SpainChallengerHard (i) Joaquín Muñoz Hernández Purav Raja Divij Sharan3–6, 6–4, [8–10]Loss1–4Ningbo, China, P.R.ChallengerHard Stefan Kozlov Jonathan Eysseric Sergiy Stakhovsky4–6, 6–7(4–7)Win2–4Spain F39, Cuevas del AlmanzoraFuturesHard Peter Bothwell Roberto Ortega Olmedo David Vega Hernández6–2, 5–7, [10–2]Win3–4Savannah, USAChallengerClay Luke Bambridge Enrique López Pérez Jeevan Nedunchezhiyan6–2, 6–2Loss3–5Zhangjiagang, China, P.R.ChallengerHard Bradley Mousley Gong Maoxin Zhang Zew/oWin4–5Kobe, JapanChallengerHard (i) Gonçalo Oliveira Li Zhe Go Soeda2–6, 6–4, [12–10]Loss4–6Nanchang, China, P.R.ChallengerClay (i) Alex Bolt Sander Arends Tristan-Samuel Weissborn2–6, 4–6Win5–6M25, Canberra, AustraliaWorld Tennis TourHard Rubin Statham Calum Puttergill Naoki Tajima6–4, 6–3Win6–6M25, Bendigo, AustraliaWorld Tennis TourHard Philip Sekulic Dane Sweeny Li Tu7–5, 6–7(7–9), [10–7]Loss6–7M25, Medellín, Colombia World Tennis TourClay Rubin Statham Benjamin Lock Courtney John Lock6−4, 4−6, [6−10]Win7–7M15, Monastir, TunisiaWorld Tennis TourHard Skander Mansouri Xin Gao Zhe Li6–3, 6–0Win8–7M25, Monastir, TunisiaWorld Tennis TourHard Aziz Dougaz Théo Arribagé Luca Sanchez7–6(7−1), 7–6(7−3)Win9–7M25, Martos, SpainWorld Tennis TourHard James Frawley Adrià Soriano Barrera Benjamín Winter López6–7(7−9), 6–3, [10−6]Loss9–8Nonthaburi, ThailandChallengerHard Christopher Rungkat Yuki Bhambri Saketh Myneni6–2, 6–7(7–9), [12–14]

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