2021 Citi Open

The 2021 Washington Open (called the Citi Open for sponsorship reasons) was a tennis tournament played on outdoor hard courts. It was the 52nd edition of the Washington Open. The event was part of the ATP Tour 500 series of the 2021 ATP Tour and part of the US Open Series leading up to the US Open grand slam in September. The Washington Open took place at the William H.G. FitzGerald Tennis Center in Washington, D.C., United States, from July 31 to August 8, 2021.

Singles

 * 🇮🇹 Jannik Sinner def. 🇺🇸 Mackenzie McDonald 7–5, 4–6, 7–5

Doubles

 * Raven Klaasen / 🇯🇵 Ben McLachlan def. 🇬🇧 Neal Skupski / 🇳🇿 Michael Venus 7–6(7–4), 6–4.

Prize money

 * per team

Seeds

 * 1 Rankings are as of July 26, 2021

Other entrants
The following players received wild cards into the singles main draw:
 * 🇺🇸 Jenson Brooksby
 * 🇪🇸 Feliciano López
 * 🇪🇸 Rafael Nadal
 * 🇺🇸 Brandon Nakashima
 * 🇺🇸 Jack Sock

The following players received entry from the singles qualifying draw:
 * 🇪🇨 Emilio Gómez
 * 🇮🇳 Prajnesh Gunneswaran
 * 🇺🇸 Mitchell Krueger
 * 🇺🇦 Illya Marchenko
 * 🇮🇳 Ramkumar Ramanathan
 * 🇸🇪 Elias Ymer

Withdrawals

 * Before the tournament
 * 🇵🇱 Hubert Hurkacz → replaced by 🇫🇮 Emil Ruusuvuori
 * 🇺🇸 John Isner → replaced by 🇮🇹 Andreas Seppi
 * 🇷🇺 Aslan Karatsev → replaced by 🇨🇴 Daniel Elahi Galán
 * 🇷🇺 Karen Khachanov → replaced by 🇺🇸 Mackenzie McDonald
 * 🇩🇪 Dominik Koepfer → replaced by 🇧🇾 Ilya Ivashka
 * 🇰🇷 Kwon Soon-woo → replaced by 🇦🇺 James Duckworth
 * 🇪🇸 Jaume Munar → replaced by Kevin Anderson
 * 🇦🇷 Guido Pella → replaced by 🇺🇸 Steve Johnson
 * 🇪🇸 Albert Ramos Viñolas → replaced by 🇦🇺 Jordan Thompson
 * 🇨🇦 Milos Raonic → replaced by Ričardas Berankis
 * 🇨🇦 Denis Shapovalov → replaced by 🇧🇾 Egor Gerasimov

Seeds

 * 1 Rankings are as of July 26, 2021

Other entrants
The following pairs received wildcards into the doubles main draw:
 * 🇦🇺 Nick Kyrgios / 🇺🇸 Frances Tiafoe
 * 🇺🇸 Sam Querrey / 🇺🇸 Jack Sock

The following pair received entry from the doubles qualifying draw:
 * 🇫🇷 Benoît Paire / 🇺🇸 Jackson Withrow

Withdrawals

 * Before the tournament
 * 🇨🇴 Juan Sebastián Cabal / 🇨🇴 Robert Farah → replaced by 🇫🇷 Fabrice Martin / 🇦🇺 Max Purcell
 * Wesley Koolhof / Jean-Julien Rojer → replaced by 🇧🇬 Grigor Dimitrov / 🇺🇸 Tommy Paul
 * 🇵🇱 Łukasz Kubot / 🇧🇷 Marcelo Melo → replaced by 🇳🇿 Marcus Daniell / 🇧🇷 Marcelo Melo
 * Nikola Mektić / Mate Pavić → replaced by  Marcelo Arévalo /  Matwé Middelkoop
 * 🇬🇧 Jamie Murray / 🇧🇷 Bruno Soares → replaced by 🇺🇸 Sebastian Korda / 🇮🇹 Jannik Sinner
 * 🇺🇸 Rajeev Ram / 🇬🇧 Joe Salisbury → replaced by 🇰🇿 Alexander Bublik / 🇰🇿 Andrey Golubev

Women's invitational
Between 2011 and 2019, the Citi Open hosted conjoining men and women tournaments. However, amid the COVID-19 pandemic in 2020, the Women's Tennis Association (WTA) revoked its sanction of the Citi Open for the year's tour and added two events to its provisional calendar instead: the Top Seed Open in Lexington, Kentucky and the Prague Open. After the Citi Open returned in 2021 from the event's eventual cancellation in the prior year, the WTA stayed its revocation of the event's sanction, so the women's tournament did not return as many women's players had scheduling conflicts with the 2020 Summer Olympics. In its place, event officials created the inaugural women's invitational as a three-day exhibition during the US Open Series. Coco Gauff, Jessica Pegula, and Jennifer Brady were the three original headliners, though Brady was later replaced by Victoria Azarenka.

The players played in a round-robin format; the winner of each pair in their first matches would then play each other in the final match. The games were played in a best-of-three set format with regular scoring and a 10-point "super tiebreak" to decide the third set. The player with the best record would be crowned the champion and in the case of a tie, the winner would be decided by the player who won the most sets or games. Because the tournament was not sanctioned by the WTA, the players would not accrue or lose any points. The prize money for the inaugural champion was set at $25,000. On August 5, Gauff defeated Azarenka in the first match, 6–3, 6–1. Azarenka was scheduled to play Pegula the following day, after Brady withdrew from the tournament, to decide the final match, but Azarenka herself later withdrew from the invitational after suffering an ankle injury. On August 7, Pegula defeated Gauff in the final match, 4–6, 7–5, [10-8], to win the invitational.