NEW YORK — So about that inflamed right shoulder that was supposed to hinder Serena Williams at the U.S. Open as she seeks a record 23rd major title: It sure seems fine.

“Definitely feels solid,” Williams said.

Not sure? There’s plenty of evidence. No need to take her word – or her coach’s – for it.

Look how Williams beat 47th-ranked Johanna Larsson 6-1, 6-1 on Saturday to reach the fourth round and collect her 307th Grand Slam match win, surpassing Martina Navratilova for most by a woman in the Open era and equaling Roger Federer for most by anyone since 1968.

Williams reached 121 mph on a serve. She had a half-dozen aces, bringing her total for the week to 31. She faced only one break point – her first of the tournament – and saved it. She smacked seven return winners. She compiled a 24-5 edge in winners.

“Tennis-wise, I think it was satisfying in all aspects. It’s not perfect, of course,” said her coach, Patrick Mouratoglou. “But for someone who didn’t play much in the last two months, I think she’s competitive.”

Now there’s an understatement.

“There is no pain. Maybe she feels a little. I don’t know; I’m not in her shoulder. But I see she plays normal. She serves normal. At practice she serves the quantity that we usually do, full power,” Mouratoglou said. “So I don’t see any problem. And she doesn’t even talk about it. I know it’s under control now.”

That sounds like bad news for upcoming opponents, starting with 52nd-ranked Yaroslava Shvedova, who advanced to the Round of 16 in New York for the first time by beating Zhang Shuai, 6-2, 7-5.

Monday’s other fourth-round women’s matchups will be Williams’ older sister, Venus, vs. No. 10 Karolina Pliskova, No. 5 Simona Halep vs. No. 11 Carla Suarez Navarro, and No. 4 Agnieszka Radwanska vs. Ana Konjuh. Venus Williams advanced comfortably Saturday night by beating No. 26 Laura Siegemund, 6-1, 6-2. In that half of the draw, only the players with the last name Williams have won a Grand Slam title; the sisters could meet in the semifinals a year after Serena eliminated Venus in the quarters.

Two past men’s champions, Andy Murray and Juan Martin del Potro, moved into the fourth round.

Murray, who won the 2012 U.S. Open, had trouble in each of the first two sets but eventually became more patient during baseline exchanges and took control for a 7-6 (4), 5-7, 6-2, 6-3 victory against Paolo Lorenzi. Murray faces No. 22 Grigor Dimitrov in the Round of 16.

Del Potro’s resurgence continued with a 7-6 (3), 6-2, 6-3 victory over No. 11 David Ferrer. The 2009 champion missed 21/2 years’ worth of major tournaments because of three operations on his left wrist and he’s ranked only 142nd, which is why he needed a wild-card invitation to get into the field.

But del Potro showed he’s back and about as good as ever, especially with his thunderous forehand, by beating Novak Djokovic and Rafael Nadal on the way to winning a silver medal for Argentina at the Rio de Janeiro Olympics last month.