NEW YORK -- Serena Williams was in pain -- "acceptable" pain, her coach called it -- after rolling her right ankle during the second set of a U.S. Open victory.
That was the bad news.
The good news for Williams as she pursues a seventh championship at Flushing Meadows and 24th Grand Slam singles title overall is that, while she reached the quarterfinals by beating No. 22 seed Petra Martic 6-3, 6-4 despite the ankle issue, No. 2 Ash Barty and No. 3 Karolina Pliskova both exited her side of the bracket Sunday.
Not that Williams seemed to care all that much about being one of only three of the top 12 seeded women who will still be around today.
"I can't afford to look at it that way. Every single match I have played, people come and they play their best. The women that I play are not generally playing at this level against other players in the locker room, so for me, I have to be the greatest, whether it's against the second seed, the No. 1 seed, or the No. 80th player in the world," said Williams, who faces No. 18 Wang Qiang next. "I have to show up or else I'm going to go home."
Williams, who turns 38 this month, appeared to be cruising along to a straightforward victory when she took an awkward step while up at the net for a volley. 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.
Still, Martic thought Williams' play might actually have improved the rest of the way.
"She started going for even more, I think. She felt like maybe she couldn't move that well anymore," Martic said. "Her shots were really precise. Serve was unbelievable. And when she hits those backhands and those first serves that well, it's not easy to play against her."
Williams ended things 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.
She plays Wang on Tuesday.
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.
Later men's matches included defending champion Novak Djokovic against Stan Wawrinka, and Daniil Medvedev against qualifier Dominik Koepfer.
Federer next takes on Grigor Dimitrov, a two-time major semifinalist who is unseeded at Flushing Meadows.
Currently coached by Andre Agassi and Radek Stepanek, Dimitrov eliminated Alex de Minaur 7-5, 6-3, 6-4 to reach his first U.S. Open quarterfinal.
Federer is 7-0 against Dimitrov.
"Given the history of me and Roger, how we've played the past years," Dimitrov said, "nothing (favors) me."