(Photo credit: Robert Deutsch-Imagn Images)

Venus Williams, returning to the Grand Slam singles stage for the first time since 2023, competed well but fell short on Monday in the first round of the U.S. Open in New York.

The 45-year-old star lost 6-3, 2-6, 6-1 to 11th-seeded Karolina Muchova of the Czech Republic in exactly two hours.

Williams, a seven-time major singles champion, became the oldest singles player at the U.S. Open since Renee Richards, then 47, lost in the first round of women's singles in 1981.

After Muchova took the first set, Williams broke serve to start the second set, then added another break for 5-2 before leveling the match. However, Muchova, 29, won the first three games of the third set, during which she never faced a break point.

'She's such a legend of our sport,' Muchova, a U.S. Open semifinalist each of the past two years, said of Williams.

The day's biggest upset saw Mexico's Renata Zarazua edge No. 6 seed Madison Keys 6-7 (10), 7-6 (3), 7-5.

It was the first victory over a top-20 player in Zarazua's career as she grabbed her head in disbelief after securing the win. She is the first Mexican woman ever to defeat a top-10 opponent at the U.S. Open.

'Coming into the match I was like almost crying because I was really nervous,' Zarazua said. 'The crowd made it so chill for me so I was loosening up.'

Zarazua took advantage of 89 unforced errors from Keys and won despite her opponent's 46-8 advantage in winners. Zarazua gave away only 34 points.

Hungary's Anna Bondar, ranked No. 97 in the world, took advantage of shaky play by No. 12 Elina Svitolina and upset the Ukrainian, 6-2, 6-4.

Two-time major champion Barbora Krejcikova ousted No. 22 seed Victoria Mboko in straight sets with a 6-3, 6-2 victory.

Mboko, the 18-year-old Canadian who won her first WTA title of any kind at the National Bank Open in her home country earlier this month, struggled with her right wrist heavily taped. While she landed 64 percent of her first serves, Mboko also suffered from 10 double faults while winning only 36 of her 70 service points.

Krejcikova, 29, entered the U.S. Open unranked but is coming off a run to the fourth round of the Cincinnati Open. The Wimbledon champion in 2024 and winner of the 2021 French Open, Krejcikova dominated from the outset against Mboko, winning 69 total points to her opponents' 49.

Krejcikova will next face unranked Moyuka Uchijima from Japan in the second round.

'I've been really busy, we've been really practicing and also we enjoyed the city,' Krejcikova said in her on-court interview after the match. 'We discovered a lot of good ice creams around the city and a lot of nice restaurants.

'I'm enjoying it. So, it's been good, and I hope I can be here as long as I can.'

No. 9 seed Elena Rybakina of Kazakhstan finished off Julieta Pareja 6-3, 6-0 to advance, while No. 17 seed Liudmila Samsonova of Russia also moved on by rallying for a 2-6, 6-4, 6-4 victory over China's Yuan Yue.

No. 30 seed Dayana Yastremska of Ukraine was eliminated 6-7 (5), 7-6 (5), 6-4 by Russia's Anastasia Pavlyuchenkova despite having 43 winners to 19 for her opponent. Yastremska was undone by 53 unforced errors.

Fifth-seeded Mirra Andreeva of Russia cruised past Alycia Parks 6-0, 6-1. Also advancing were No. 15 Daria Kasatkina of Australia, No. 19 Elise Mertens of Belgium, No. 28 Magdalena Frech of Poland and No. 29 Anna Kalinskaya of Russia.

--Field Level Media