2021 San Diego Open

The 2021 San Diego Open was a men's tennis tournament played on outdoor hard courts. It was the 1st edition of the San Diego Open, and part of the ATP Tour 250 series of the 2021 ATP Tour.

It was primarily organized due to the cancellation of Asian tournaments during the 2021 season, because of the ongoing COVID-19 pandemic. Positioned one week before the 1000 Indian Wells Masters and only a 2-hour 30 min drive from Indian Wells, the San Diego Open attracted a very strong line up of players including Denis Shapovalov, Andrey Rublev, Grigor Dimitrov and Andy Murray. With 8 of the top 20 players attending and the ranking cut off being 42 to get into the main draw it was the second most competitive ATP 250 all season since Doha.

It was held at the Barnes Tennis Center in San Diego, United States, from September 27 until October 3, 2021. Daniel Vallverdu took on the position of managing director, Ryan Redondo was named the tournament director and Billie Jean King accepted the role of honorary tournament chair.

After beating Dimitrov in the semifinal Casper Ruud went on to win the final of the 2021 San Diego Open beating Cameron Norrie 6-0 6-2 and was handed the trophy by Rod Laver. It was Ruud's fifth victory of the season.

Singles

 * 🇳🇴 Casper Ruud def. 🇬🇧 Cameron Norrie, 6–0, 6–2

Doubles

 * 🇬🇧 Joe Salisbury / 🇬🇧 Neal Skupski def. 🇦🇺 John Peers / 🇸🇰 Filip Polášek, 7–6(7–2), 3–6, [10–5]

Seeds

 * 1 Rankings are as of 20 September 2021.

Other entrants
The following players received wildcards into the main draw:
 * 🇬🇧 Andy Murray
 * 🇺🇸 Brandon Nakashima
 * 🇯🇵 Kei Nishikori

The following player received entry as a special exempt:
 * 🇰🇷 Kwon Soon-woo

The following players received entry from the qualifying draw:
 * 🇦🇺 Alex Bolt
 * 🇮🇹 Salvatore Caruso
 * 🇺🇸 Christopher Eubanks
 * 🇮🇹 Federico Gaio

The following players received entry as lucky losers:
 * Kevin Anderson
 * August Holmgren
 * 🇺🇸 Denis Kudla

Withdrawals

 * Before the tournament
 * 🇨🇦 Félix Auger-Aliassime → replaced by August Holmgren
 * Cristian Garín → replaced by 🇩🇪 Dominik Koepfer
 * 🇧🇪 David Goffin → replaced by 🇺🇸 Sebastian Korda
 * 🇰🇷 Kwon Soon-woo → replaced by Kevin Anderson
 * 🇷🇸 Dušan Lajović → replaced by Lloyd Harris
 * 🇯🇵 Kei Nishikori → replaced by 🇺🇸 Denis Kudla
 * 🇺🇸 Reilly Opelka → replaced by 🇦🇷 Federico Delbonis

Seeds

 * 1 Rankings are as of 20 September 2021.

Other entrants
The following pairs received wildcards into the doubles main draw:
 * 🇺🇸 Brandon Nakashima / Sem Verbeek
 * Antonio Šančić / 🇳🇿 Artem Sitak

Withdrawals

 * Before the tournament
 * 🇺🇸 Nicholas Monroe / 🇺🇸 Frances Tiafoe → replaced by 🇩🇪 Dominik Koepfer / 🇺🇸 Nicholas Monroe
 * 🇺🇸 Rajeev Ram / 🇺🇸 Jack Sock → replaced by 🇦🇺 Jordan Thompson / 🇺🇸 Jackson Withrow