The 2021 San Diego Open was a men's tennis tournament played on outdoor hard courts.

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.

[1] 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.