Serena Williams will still get a decent day's rest on the middle Sunday at Wimbledon.

The defending 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.

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''Was it? Cool. Oh, nice,'' she said with a laugh. ''I had no idea. 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 and now ranks second in the Open era behind Martina Navratilova, who went 306-49.

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.

''Obviously I love having that Sunday off but I'm a little behind in my matches, so I guess I had to play an extra day,'' Williams said.

She didn't have to work very hard as she completely dominated the 43rd-ranked Beck, who has never been past the third round here.

After falling an early break behind at 2-1, Williams won 11 of the last 12 games and 24 of the second set's 28 points. She finished the first set with one of her seven aces and served out the match at love.

Williams will next face No. 13 Svetlana Kuznetsova, who came from behind to beat No. 22 Sloane Stephens 6-7 (1), 6-2, 8-6 to reach the fourth round at Wimbledon for the first time since 2008. The 2 1/2-hour match started on No. 1 Court long before Williams and Beck began play on Centre - and finished after.

Kuznetsova, a two-time Grand Slam champion, has reached the quarterfinals here three times, but the last time was back in 2007.

CoCo Vandeweghe, making a strong run at Wimbledon for the second year in a row, beat No. 7 Roberta Vinci of Italy 6-3, 6-4 in the first match on Centre Court. The 27th-seeded American advanced to the quarterfinals here last year before losing to Maria Sharapova in three sets. This is the first time she's been seeded at a Grand Slam.

''Roberta's a really tough opponent,'' Vandeweghe said. ''She has a lot of craftiness to her game that you don't see too much. She makes you beat her. So that's what I tried to do, stay focused and keep pressing.''

Her fourth-round opponent will be 23rd-seed Anastasia Pavlyuchenkova of Russia, who downed No. 11 Timea Bacsinszky of Switzerland 6-3, 6-2. Bacsinszky made it to the quarterfinals last year, but failed to break serve once on Sunday.

Also advancing was 50th-ranked Elena Vesnina, who beat 225th-ranked American qualifier Julia Boserup 7-5, 7-5. The Russian previously reached the fourth round here in 2009.

All 22,000 tickets for Sunday's play were snapped up in 27 minutes when they went on sale online on Saturday.

The tournament is still reverberating from the stunning exit of Novak Djokovic, whose bid for a fifth consecutive major title and the third leg of a calendar-year Grand Slam was stopped by American Sam Querrey in the third round.