NEW YORK -- Second-seeded Ash Barty overcame a slow start and a shaky serve to survive a first-round scare on a packed opening day of the US Open.
Barty, the French Open champion, amassed 36 unforced errors and got fewer than half her first serves in en route to a 1-6, 6-3, 6-2 victory over 80th-ranked Zarina Diyas of Kazakhstan on Monday.
The Australian lost the first set in a mere 28 minutes and did not begin to come alive until the match was knotted at 3-3 in the second. She went on to win nine of the last 11 games, ending the match when Diyas sailed a forehand long.
"I was happy with the way I was able to fight through after a pretty awful start," Barty said. "Not the ideal start. Not the perfect start. But it is what it is."
Kristina Mladenovic of France defeated No. 14 seed and 2016 US Open champion Angelique Kerber 7-5, 0-6, 6-4. Kerber's first-round loss follows second-round exits at both the French Open and Wimbledon this year.
Venus Williams, meanwhile, tied Martina Navratilova's record by playing in the US Open for the 21st time on Monday. She improved to 21-0 0 in first-round matches at Flushing Meadows by beating Zheng Saisai 6-1, 6-0 in all of 66 minutes in Louis Armstrong Stadium.
"I was happy with today,'' Williams said, "so I'm not going to ask for more.''
Williams is a two-time champion in New York -- in 2000 and 2001 -- and owns seven Grand Slam singles titles, along with another 14 in doubles. However, she is 39 and lost in the first round at the French Open and Wimbledon this year, and her ranking is down to No. 52. That puts her 14 spots behind Zheng.
It sure didn't seem that way on this afternoon, though. Williams dominated from beginning to end, winning twice as many total points, 58-29, and compiling more than four times as many winners, 25-6, and two fewer unforced errors than her opponent.
Williams also showed off her big serve, reaching 121 mph, and set up a match against No. 5 seed Elina Svitolina.
For years, as her ranking has slipped further from the No. 1 spot she once briefly held and her results have been less than what they once were, Williams has faced questions about retirement. She never really paid them any heed, often saying that she thinks she has more to give to the sport.
On Monday, she sure looked and sounded as if she still does.
"It's a wonderful job, and it's all-consuming. So if you don't love it, it's really hard to do well at it,'' Williams said. "And the fact that I have done well has shown that I have loved it and will love it, and I'll always love it. Even when it's all over, I'll still be a tennis player."
In other results, No. 12 seed Anastasija Sevastova beat Eugenie Bouchard, a former Wimbledon finalist and top-10 player 6-3, 6-3. Former Olympic gold medalist Monica Puig fell by the same score to Rebecca Peterson of Sweden. Russian Ekaterina Alexandrova defeated 2011 US Open champ Samantha Stosur 6-1, 6-3.
The Associated Press contributed to this report.