Venus Williams came quite close to making a winning return at the Citi Open, but fell just short in the end. Fellow Grand Slam champion Andy Murray also ended up bowing out of the tournament in the first round.
Elsewhere, Emma Raducanu's doubles debut on the WTA tour ended with a straight-sets loss. Reigning Wimbledon champion Elena Rybakina was defeated by Daria Kasatkina at the Silicon Valley Classic in her first match since winning the title.
Meanwhile, Alexander Zverev shared a throwback post commemorating a year of him winning the gold medal at last year's Tokyo Olympics.
Here's a round-up of the day's headlines:
Venus Williams loses comeback match at Citi Open despite taking first set
Seven-time Grand Slam champion Venus Williams returned to singles action after a year at the Citi Open.
Up against Rebecca Marino in the first round, she was off to a good start as she claimed the opening set. The Canadian then raised her level to take the second set and force a decider.
Williams appeared to be back on track and on the cusp of victory as she led 4-1 in the third set. However, Marino staged a comeback and won the next five games to win the match 4-6, 6-1, 6-4.
Williams will look to secure her first win of the season when she competes at next week's Canadian Open.
Andy Murray upset in first round of the Citi Open
Former World No. 1 Andy Murray was stunned by Mikael Ymer in the first round of the Citi Open.
The Brit lost a closely contested opening set despite holding multiple set points. He trailed in the second set, but staged a comeback to clinch it. However, Murray was unable to sustain momentum.
The deciding set was quite one-sided, with Ymer easily coming out on top to win the match 7-6 (8), 4-6, 6-1.
Emma Raducanu's doubles debut ends in a defeat
2021 US Open champion Emma Raducanu teamed up with fellow teenager Clara Tauson to compete in a doubles match for the first time at the Citi Open.
Up against the veteran pairing of Lucie Hradecka and Monica Niculescu, the two youngsters put up a fight but ultimately came up short, losing 6-4, 6-1.
Raducanu will take on Louisa Chirico in the first round of the singles event at the Citi Open on Tuesday evening.
Alexander Zverev reminisces about his Olympic triumph
Alexander Zverev achieved one of his biggest career goals by winning the Olympic gold medal at last year's Tokyo Olympics. He took to Instagram to share a throwback post of his historic achievement and captioned it:
"One year ago, we brought the 🥇home 🇩🇪 The moment a lifetime of hard work payed off, and the memory will last a lifetime."
Zverev is currently sidelined due to an ankle injury he sustained at the French Open. There is no timeline for his return to the tour for now.
Wimbledon champion Elena Rybakina loses in first round of Silicon Valley Classic
Elena Rybakina won her maiden Grand Slam title at Wimbledon a few weeks ago. She returned to action for the first time since her Major triumph at the Silicon Valley Classic.
Up against Daria Kasatkina in the first round, she took the opening set in a dominant manner. However, Rybakina only managed to win a couple of games after that as Kasatkina staged a comeback to win 1-6, 6-2, 6-0.
The Kazakh's game fell apart spectacularly as the match progressed and had no answer to her opponent's tactics.
Rybakina will look to make amends at at the Canadian Open in Toronto next week.
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