23:52 CET - Big-serving American Reilly Opelka is through to the second round on the men's side in Washington after downing Murphy Cassone 7-6, 6-7, 6-3. Learner Tien has also won his opening match.
There are just a few men's matches left in the day in the American capital - you can follow the rest of the overnight action here.
That's all from us today on the Tennis Tracker, but be sure to tune in again tomorrow as the matches roll on in Washington, Prague, Kitzbuhel and Umag.
23:11 CET - In the last match of the day in Kitzbuhel, sixth seed Arthur Rinderknech has beaten Facundo Bagnis of Argentina 7-6, 4-6, 6-3.
Catch up on all the results from Kitzbuhel here.
22:43 CET - Venus Williams is a winner once again! The 45-year-old legend has won her opening doubles match in Washington, playing alongside Hailey Baptiste.
The American duo toppled Canada's once-hyped Eugenie Bouchard and American Ngounoue Clervie 6-3, 6-1.
Venus begins her singles campaign tomorrow, taking on Peyton Stearns.
22:37 CET - Nick Kyrgios and Gael Monfils teamed up as an exciting doubles duo for the Washington Open. However, their tournament is already over, with the pair losing their opening match to Hugo Nys and Edouard Roger-Vasselin, who came out on top 6-2, 6-2.
22:24 CET - In the day's last match in Umag, Swiss veteran Stan Wawrinka has brushed aside Ecuador's Alvaro Guillen Meza 6-4, 6-1 to move into the second round.
Over in Washington, Cameron Norrie has defeated fellow Brit Bily Harris 6-3, 7-6 to advance.
22:00 CET - Tennis legend Venus Williams is on court in Washington, playing doubles alongside Hailey Baptiste against Eugenie Bouchard and Ngounoue Clervie.
You can follow that match here.
21:50 CET - Fifth seed Mariano Navone is through to the second round in Umag after defeating Tomas Barrios Vera 6-1, 6-2.
Over in Kitzbuhel, qualifier Norbert Gombos has stunned Hugo Gaston 6-3, 6-4 to advance.
21:25 CET - Moving back to Washington, British veteran Daniel Evans has edged Zizou Bergs 3-6, 6-4, 6-3 to move into the second round. Mackenzie McDonald has also won to go through.
Over in Umag, Nikoloz Basilashvili has stunned sixth seed Roberto Carballes Baena 6-3, 6-4 to book his spot in the second round.
20:46 CET - Second seed Rebecca Sramkova has beaten Jesika Maleckova 6-3, 4-6, 6-4 in the final match of the day at the Livesport Prague Open.
Catch up on all the scores from Prague here.
20:29 CET - In the second of the only two women's singles matches in Washington today, Canada's Leylah Fernandez has beaten Australian Maya Joint 6-3, 6-3 to move into the next round.
Next up for Fernandez is a meeting with top seed Jessica Pegula.
20:10 CET - Back to Washington, Alexandre Muller has beaten Beibit Zhukayev 6-4, 6-4 to set up a second-round meeting with third seed Holger Rune.
20:07 CET - A couple more matches have wrapped up in Umag with Frenchmen Terence Atmane and Titouan Droguet both winning to progress to the second round.
19:59 CET - Matteo Arnaldi has progressed in Washington, with the Italian coming from behind and saving four match points to defeat Daniel Altmaier 4-6, 6-2, 7-6(2).
Elsewhere, Pablo Llamas Ruiz is through in Umag after a comfortable 6-2, 6-4 triumph over Kamil Majchrzak, while Marton Fucsovics proved too strong for wildcard Joel Josef Schwaerzler in Kitzbuhel, coming through 6-2, 2-6, 6-3.
19:21 CET - Canadian teenager Victoria Mboko is through to the second round in Washington after a fairly routine 6-2, 6-4 victory over Anastasia Potapova.
18:48 CET - Alexander Shevchenko is the latest winner in Kitzbuhel, with the Kazakh recovering from a set down to outlast Daniel Elahi Galan, 2-6, 6-3, 6-4.
18:33 CET - Hungary's Fabian Marozsan has advanced in Washington, battling through a competitive opening set to see off the challenge of Benjamin Bonzi, 7-5, 6-1.
18:25 CET - Tseng Chun-hsin is the first winner of the day in Umag after a hard-fought 7-5, 6-4 triumph over Giulio Zeppieri.
Meanwhile, in Washington, home favourite Ethan Quinn has progressed to the next round courtesy of a convincing 6-3, 6-2 victory against Christopher O'Connell.
17:58 CET - Seventh seed Francisco Comesana is safely through in Kitzbuhel, with the Argentine defeating Tristan Boyer in straight sets, 6-3, 7-6(1).
16:24 CET - Elisabetta Cocciaretto and Lucrezia Stefanini are the latest winners in Prague, having secured straight-set victories over Vikorija Golubic and Vikoriya Tomova, respectively.
14:18 CET - Two more matches have wrapped up in Prague with ninth seed Ann Li beating Astra Sharma 7-6, 6-3, while Sara Bejlek has upset Moyuka Uchijima 7-5, 6-2 to also advance to the second round.
Over in Kitzbuhel, play is interrupted due to heavy rainfall.
12:32 CET - The first winners of the day in Prague are home favourite Marie Bouzkova and eighth seed Alycia Parks, who both claimed very straightforward victories to move into the second round.
09:53 CET - We're just over an hour away from play getting started for the day, as fifth seed and home favourite Marie Bouzkova takes on Xinyu Gao in Prague and Francisco Comesana faces Tristan Boyer in Kitzbuhel.
Later on, the ATP and WTA 500 tournaments in Washington get underway, with Danielle Collins, Leylah Fernandez and Cameron Norrie the standout names involved today.
Check out the full schedule for events in Washington (ATP), Washington (WTA), Prague, Kitzbuhel and Umag via the links.
09:35 CET - Good morning and welcome to our coverage of today's tennis!