Williams beat 19-year-old Naomi Osaka of Japan 7-6 (3), 6-4 in the third round, and will face another 19-year-old on Monday with a quarterfinal berth at stake, Ana Konjuh of Croatia.
The 10th-seeded Williams is a five-time champion at the All England Club.
This is her first tournament since a two-car crash in Florida last month that police say she caused. A 78-year-old man in the other car died about two weeks later.
"I've had to step it up. I imagine that's going to continue," Williams said. "All I can do is try to be my best."
Nadal gets through to fourth round
Rafael Nadal is on his way to the fourth round at Wimbledon, and he's three matches away from taking over as the No. 1 player in the world.
Nadal beat Karen Khachanov of Russia 6-1, 6-4, 7-6 (3) Friday on Centre Court. If he reaches the final at the All England Club, the two-time Wimbledon champion will take over from
"First set and a half, I think, was very, very well. Very happy (with) the way that I played," Nadal said in a television interview after walking off court. "Then it was a little bit tougher. I think I stopped a little bit with the legs and he started to hit stronger, but he's still a tough opponent and it's impossible to win easy."
On Monday, Nadal will face Gilles Muller in the fourth round. Muller beat Nadal at the All England Club in 2005, but the Spaniard got one back in 2011. That was the last time Nadal got past the fourth round at Wimbledon, reaching the final but losing to Novak Djokovic.
The third-round match between 12th-seeded
Querrey was leading Tsonga, a two-time Wimbledon semifinalist and 2008
The match will resume not before 1 p.m. on the same court on Saturday. The winner will face
Murray, the defending champion, held on through a tough fourth set to beat
Murray has won the title at the All England Club twice, but he entered this year's tournament after canceling a pair of exhibition matches because of an ailing left hip.
Azarenka wins again
Earlier Friday, Victoria Azarenka extended her Grand Slam comeback into the second week.
The former No. 1 from Belarus, who gave birth to her first child in December, advanced to the fourth round by beating Heather Watson 3-6, 6-1, 6-4 on Centre Court.
Azarenka also lost the first set in her opening match, but that was only her third match since her return. Friday's match was her fifth.
"This is the matches that you're looking for," Azarenka said, "try to find a way when not everything goes great."
The two-time Grand Slam champion will next face Simona Halep on Monday in the fourth round. The second-seeded Romanian beat Peng Shuai 6-4, 7-6 (7).
Fourth-seeded Elina Svitolina, sixth-seeded Johanna Konta, 21st-seeded Caroline Garcia and 27th-seeded Ana Konjuh also reached the fourth round.
For the men, ninth-seeded
"I couldn't maintain my level high enough," Nishikori said. "He served well every set. Was really tough time (on) my return game."
Marin Cilic, the man who beat Nishikori in that U.S. Open final, advanced to the third round by beating Steve Johnson 6-4, 7-6 (3), 6-4. The seventh-seeded Croat will next face Bautista Agut on Monday.
4:10 p.m.: This article has been updated with more results from evening matches at Wimbledon.