In men's draw there are wins for Alexander Zverev and Gael Monfils
Mixed fortunes for Williams sisters at Wimbledon as Serena wins after Venus loses
Serena Williams was given a thorough workout but made it through to the second week of Wimbledon.
The seven-time champion beat Kristina Mladenovic 7-5, 7-6 just minutes after her sister Venus went out of the tournament over on Court One to Kiki Bertens.
Mladenovic served for the first set, but Williams survived and then stepped up in the second-set tie-break to move into the fourth round and a match on Monday against Russian Evgeniya Rodina, who shocked Madison Keys in her third round win.
Williams has been feeling her way into the tournament but it was clear that she was facing her toughest test yet when Mladenovic took an early break.
An important moment came when Williams was serving at 4-2 behind, when at 15-30 the American looked to have sent the ball long to give Mladenovic two double-break points.
But Williams challenged and it proved an inspired decision as Hawk-Eye showed the ball to be a couple of millimetres in.
The Frenchwoman, ranked 62nd in the world, still had a chance to serve for the first set, but inevitably Williams broke.
That was the start of a run of six games in a row that gave her the first set and a break in the second.
Mladenovic battled back to level up and it went with serve until a tie-break, where the former world number one raised her game.
This is only her fourth tournament back since giving birth last September and Williams is pleased with her progress.
"I am really happy," she said.
"It's my serious second tournament back so it is going pretty well.
"I have worked really, really, really hard and it has been a long arduous road. I always expect to come out and do the best I can do and that's all I can hope for."
Meanwhile, Venus, a five-time Wimbledon champion, was beaten 6-2, 6-7, 8-6 by Bertens.
Of the loss, she said: "I just ran out of time in the end. She played really well, you have to win the last point and I didn't succeed in that today.
"The third set was really competitive, it was just toe-to-toe.
"Of course, you know that the plan is to go out and try and win the matches. I think she was a little bit luckier than I was in the end. Sometimes it takes luck and skill and she definitely deserved to win."
In the men's draw, fourth seed Alexander Zverev survived a scare as he came from two sets to one down to defeat Taylor Fritz 6-4, 5-7, 6-7, 6-1, 6-2.
Sam Querrey, the No 11 seed, reached the semi-finals 12 months ago but there will be no repeat this year as he lost 5-7, 6-4, 6-4, 6-2 to Gael Monfils.