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Serena Williams of the U.S returns to Annika Beck of Germany during their women’s singles match on day seven of the Wimbledon Tennis Championships in London, Sunday, July 3, 2016. (AP Photo/Alastair Grant)

LONDON (AP) — Serena Williams earned a decent day’s rest on the middle Sunday at Wimbledon, while Jo-Wilfried Tsonga had to work overtime — 19-17 in the fifth set — in another marathon involving John Isner.

Williams, the defending women’s champion and six-time winner, overwhelmed Annika Beck 6-3, 6-0 in just 51 minutes on Centre Court early Sunday afternoon, advancing to the fourth round with her 300th career Grand Slam match win.

Williams, who compiled a 25-2 edge in winners, wasn’t aware of the 300-win milestone until she was asked about it in a post-match interview.

“I had no idea,” she said. “That’s awesome, right? That’s good, right? I think that’s a lot of matches.”

Williams’ latest win breaks a tie at 299 wins with Chris Evert. She now ranks second in the Open era behind Martina Navratilova, who went 306-49.

Williams, who is bidding to equal Steffi Graf’s Open era record of 22 Grand Slam titles, was asked about the pressure of being expected to win all the time.

“Every time I step out on the court, if I don’t win, it’s major national news,” she said. “But if I do win, it’s just like a small tag in the corner. … I don’t look at it as a burden. I look at it almost like something that’s really awesome to be in that position.”

For only the fourth time in Wimbledon’s 139-year history, play was scheduled on the middle Sunday, which is the traditional rest day, because of rain delays in the first week that caused a backlog of matches.

While Williams played just 15 games in under an hour, Tsonga and Isner needed 44 games and 2 hours, 33 minutes to complete the final two sets of their suspended third-round match. The final set featured 36 games and lasted 2 hours, 8 minutes.

“It’s good to be alive,” said Tsonga, who saved a match point at 16-15 in the fifth before overcoming the American 6-7 (3), 3-6, 7-6 (5), 6-2, 19-17.

Isner led two sets to one when play suspended because of darkness on Saturday. The match lasted a total of 4 hours, 24 minutes on Court 2.

That’s still modest compared to Isner’s win over France’s Nicolas Mahut six years ago. He prevailed 70-68 in the final set of the longest match in tennis history, which lasted more than 11 hours over three days in the first round.

Tsonga, a Frenchman seeded No. 12, got the only break of Sunday’s fifth set to go ahead 18-17. He then served out the match at 15, hitting a running backhand cross-court volley into the open court to close it out. He hopped up and down and swung both arms in celebration as the crowd erupted.

It was Tsonga’s 103rd match win in a Grand Slam, putting him in a tie with Jean Borotra at the top of the list of French players with the most victories in majors.

Tsonga’s next opponent will be countryman and No. 7 Richard Gasquet, who downed Albert Ramos-Vinolas of Spain, 2-6, 7-6 (5), 6-2, 6-3.

Another Frenchman, No. 32 Lucas Pouille, ended the Grand Slam comeback of Juan Martin del Potro, beating the Argentine 6-7 (4), 7-6 (6), 7-5, 6-1. The 22-year-old Pouille had never won a tour-level match on grass until this tournament. Del Potro was making his first appearance at Wimbledon since 2013 after a series of surgeries on his left wrist.

It’s the first time since 1929 that four Frenchmen have reached the round of 16 at Wimbledon.

Nick Kyrgios, an Australian seeded No. 15, set up a marquee fourth-round matchup against No. 2 Andy Murray, defeating Feliciano Lopez 6-3, 6-7 (2), 6-3, 6-4. Kyrgios, who served out the match after receiving a time delay warning, made it to the quarterfinals as a wild card in 2014.

An all-Czech matchup was assured in the fourth round when No. 10 Tomas Berdych and Jiri Vesely both advanced. Berdych, the Wimbledon runner-up in 2010, beat 19-year-old rising German star Alexander Zverev 6-3, 6-4, 4-6, 6-1, while Vesely swept Portugal’s Joao Sousa 6-2, 6-2, 7-5.

Williams will next face No. 13 Svetlana Kuznetsova, who came from 5-2 down in the final set to beat No. 22 Sloane Stephens 6-7 (1), 6-2, 8-6 and reach the fourth round for the first time since 2008.

Williams has a 9-3 career record against Kuznetsova, but the two-time Grand Slam champion from Russia beat her this year on hard courts in Miami.

“She knows my game, I know her game,” Williams said. “It’s just really down to who’s really going to fight to win it.”

CoCo Vandeweghe beat No. 7 Roberta Vinci of Italy 6-3, 6-4. The 27th-seeded American advanced to the quarterfinals here last year before losing to Maria Sharapova in three sets.

Her fourth-round opponent will be 23rd-seed Anastasia Pavlyuchenkova of Russia, who downed No. 11 Timea Bacsinszky of Switzerland 6-3, 6-2.

Also advancing was 50th-ranked Elena Vesnina, who beat 225th-ranked American qualifier Julia Boserup 7-5, 7-5. She’ll next play fellow Russian Ekaterina Makarova, a 6-4, 6-2 winner over No. 24 Barbora Strycova.