Stefanos Tsitsipas of Greece returns a shot from Jordan Thompson of Australia during Day 4 of the Citi Open at Rock Creek Tennis Center on August 1, 2019 in Washington, DC. (Photo by Mitchell Layton/Getty Images)

The Citi Open is a fan-favorite during the US Open Series, taking place in the capital of the United States and boasting fast hard courts that make matches all the more exciting. This year's edition of the tournament is almost over, but that doesn't mean that fans can slack on their knowledge.

Back-to-back defending champion Alexander Zverev did not return this year to Washington to defend his title, but there are plenty of players that were eager to take his spot. Stefanos Tstsipas, as the first seed, is still in the running and will face Nick Kyrgios in the semifinals.

See how much you know about the Citi Open, from its original name to the recent winners.