Venus Williams still loves her job. And she's still capable of doing it rather well.

Playing in the U.S. Open for the 21st time, tying Martina Navratilova's record, Williams improved to 21-0 in first-round matches at Flushing Meadows by beating Zheng Saisai 6-1, 6-0 in all of 66 minutes in Louis Armstrong Stadium on Monday.

"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 — back in 2000 and 2001 — and owns seven Grand Slam singles titles in all, along with another 14 in doubles. But she's also 39, had 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.

Sure didn't seem that way on this afternoon. Williams dominated from beginning to end, winning twice as many total points, 58-29, 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 next.

For years, as her ranking has slipped further away from the No. 1 spot she once briefly held, and her results have been less than what they once were, Williams repeatedly has faced questions about whether she was considering retirement. She never really paid any heed to that, often saying that she feels she has more to give to the sport.

And 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."

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OPELKA DOES IT AGAIN

Reilly Opelka is making a habit of eliminating seeded players at Grand Slam tournaments. The 6-foot-11 (2.11-meter) American's latest such win came in his main-draw debut at the U.S. Open, against No. 11 Fabio Fognini of Italy.

That 6-3, 6-4, 6-7 (6), 6-3 victory Monday on Court 17 came courtesy not so much of Opelka's booming serve, although he did smack 26 aces, but his impressive performance at the baseline, including thanks to a backhand Fognini called "very strange."

Opelka, currently ranked a career-high 42nd, acknowledged that his serve wasn't at its very best, but said the victory "shows that I've got more than that to back it up."

This follows a win over John Isner at the Australian Open in January and over three-time major champion Stan Wawrinka at Wimbledon in July, when Opelka reached the third round for the first time at a major.

"I've done a great job staying within myself, within my limits, against those guys," said Opelka, who turns 22 on Wednesday, when he'll play his second-round match. "The margins, the gap, is so small between top 10 and top 20 and whatnot. For example, today, I did a great job of staying within myself."

The only real slip-up by Opelka on Monday came when he served for the match ahead 6-5 in the third set. Still, after getting broken there and eventually dropping that set, Opelka recovered quickly to grab the fourth.

"Players like that," Fognini said, "make you play badly and they put you under pressure."

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BYE, KERBER

Angelique Kerber seems to alternate good Grand Slam years with bad ones. This was a bad one.

The three-time major champion and former No. 1 bowed out of the U.S. Open in the first round Monday, beaten by Kristina Mladenovic 7-5, 0-6, 6-4.

Kerber, who was seeded 14th, won more points, 105-93 thanks to the way she controlled the second set, but just couldn't hang in there down the stretch.

This comes after a second-round loss at Wimbledon, which followed a first-round loss at the French Open.

In 2016, Kerber won the Australian Open and U.S. Open for her first two Slam titles. In 2017, though, she had a pair of first-round exits at majors. In 2018, Kerber won Wimbledon and reached another Slam semifinal. Now she'll hope the pattern continues in 2020 after a disappointing 2019.

"Not really the best year for Grand Slams for me," she said.