NEW YORK (AP) -- Serena Williams seemingly was cruising along to a straightforward victory in the U.S. Open's fourth round when she took an awkward step while up at the net for a volley and twisted her right ankle.
She tumbled to the ground and sat there, cross-legged, right in the middle of Arthur Ashe Stadium for a few moments. Williams has dealt with various health issues all season, including one that ended her stay at the Australian Open.
Might that sort of thing be happening again? Williams immediately asked for a trainer, who added tape to her lower right leg and foot during a medical timeout at the ensuing changeover midway through the second set Sunday. Soon enough, Williams was back on course, beating No. 22 seed Petra Martic 6-3, 6-4 to reach the quarterfinals at Flushing Meadows for her 11th appearance in a row.
"I just rolled it. I don't know why," said Williams, who will face No. 18 Wang Qiang of China next. "I was volleying and it just went over, so that was a little frustrating."
Never really slowed her down, though. A couple of points after falling, she got the last service break she would need with a drop volley winner that made it 3-2.
She ended this match by raising both arms after smacking an ace at 118 mph, her fastest of the afternoon, punctuating an overpowering performance that included 38 winners to Martic's 11.
"It's been a rough year with injuries," said the 37-year-old Williams, who owns six U.S. Open titles and 23 Grand Slam singles trophies in all, "so I thought, 'Oh, no, not again!'"
The scene Sunday brought back memories of Williams' Australian Open quarterfinal in January against Karolina Pliskova. Williams was way ahead -- holding a match point at 5-1, 40-30 in the third set -- when she turned her left ankle awkwardly. From there, Williams was no longer, well, Williams, dropping every point she served the rest of the way.
She failed to convert four match points in all that day, ceded six games in a row and lost 7-5 in the third. That time, Williams didn't call for a trainer, which surprised many. Didn't make that mistake this time.
Williams has not managed to complete a non-Slam tournament in 2019, withdrawing from each with one ailment or another, including a viral illness, a hurt left knee and, most recently, back spasms. She hasn't won a title since returning to the tour after having a baby; her daughter, Olympia, was born exactly two years ago Sunday.
"Best day of my life," Williams called it.
Wang, who never had played in the fourth round at a major until Sunday, advanced by surprising No. 2 seed and reigning French Open champion Ash Barty 6-2, 6-4.
Pliskova, the 2016 U.S. Open runner-up who was seeded No. 3, departed, too, with a 6-7 (1), 6-3, 7-5 loss over nearly 2 1/2 hours against 16th-seeded Johanna Konta of Britain.
This is the only Grand Slam tournament where Konta has yet to reach the semifinals; she'll now meet No. 5 Elina Svitolina of Ukraine or No. 10 Madison Keys of the U.S., who were scheduled to play Sunday night.
Earlier Sunday, Roger Federer kept up his recent surge, dominating No. 15 seed David Goffin 6-2, 6-2, 6-0 in just 79 minutes. That's one fewer minute than it took him to put together a 6-2, 6-2, 6-1 win against Dan Evans in the previous round.
"In a fourth round like this," said Federer, who lost at that stage a year ago in New York, "if you can keep it nice, short, simple, you have to take (that)."
"You don't know why you're missing everything, easy balls," Goffin said. "All of a sudden. he's playing well."
Federer, who collected five of his men's-record 20 major championships at the U.S. Open from 2004-08, next takes on Grigor Dimitrov, a two-time major semifinalist who is unseeded at Flushing Meadows.
Dimitrov eliminated Alex de Minaur 7-5, 6-3, 6-4 to reach his first U.S. Open quarterfinal.