The 34-year-old American brushed aside Germany’s world number 43 Annika Beck 6-3, 6-0 on the back of 25 winners and seven aces and goes on to face long-time Russian rival Svetlana Kuznetsova.
“I thought it was good. I still want to get out to a little bit of a faster start but I was really focused and calm,” said Williams, who is just six wins short of Martina Navratilova’s Open era record of 306 Slam wins.
Williams has now won 82 matches at Wimbledon as she remains on course to equal Steffi Graf’s Open era record of 22 Grand Slam titles with her seventh Wimbledon crown.
Williams took the starring role as play was held on the middle Sunday for only the fourth time in Wimbledon history, and the first time since 2004, as organisers tried to clear the backlog caused by days of rain.
Nick Kyrgios, the Australian 15th seed, booked a last-16 clash with world number two Andy Murray after beating Feliciano Lopez 6-3, 6-7 (2/7), 6-3, 6-4 in another tie held over from Saturday at one set all.
Murray, the 2013 champion, is the top seed left in the draw after world number one Novak Djokovic was knocked out by Sam Querrey on Saturday.
“I definitely have the tools to beat Andy, but saying that, he’s probably one of the best players in the world and he’s probably the favourite at the moment since Novak is out,” Kyrgios said.
Isner going the distance again
Fans who managed to secure tickets for Sunday’s extra day of play got their money’s worth on Court Two, where Jo-Wilfried Tsonga downed US marathon man John Isner 6-7 (3/7), 3-6, 7-6 (7/5), 6-2, 19-17.
French 12th seed Tsonga, a semi-finalist in 2011 and 2012, saved a match point in the 32nd game of the final set.
The last set alone lasted more than two hours.
Isner, the 18th seed, famously won the longest tennis match ever played when he beat another Frenchman, Nicolas Mahut, 70-68 in the final set at Wimbledon in the first round in 2010.
That five-setter, stretched over three days, lasted 11 hours and five minutes.
Tsonga goes on to face fellow Frenchman Richard Gasquet for a spot in the quarter-finals.
Unseeded Czech left-hander Jiri Vesely, who beat Djokovic in Monte Carlo in April, made the fourth round of a Slam for the first time by beating Portuguese 31st seed Joao Sousa 6-2, 6-2, 7-5.
He will meet compatriot and 10th seed Tomas Berdych, the 2010 runner-up, who edged German teenager Alexander Zverev 6-3, 6-4, 4-6, 6-1.
Two-time Grand Slam champion Kuznetsova reached the Wimbledon fourth round for the first time since 2008 despite becoming involved in a row with the umpire over coaching.
The 31-year-old 13th seed battled back from 2-5 down in the final set to defeat US 18th seed Sloane Stephens 6-7 (1/7), 6-2, 8-6.
But the Russian was hit with a code violation for coaching early in the final set which prompted a bitter exchange with umpire Marijana Veljovic.
“I’m just doing my job,” said the official.
“Well, you’re not doing it very well,” responded Kuznetsova, the 2004 US Open champion and 2009 French Open winner.
Russian 21st seed Anastasia Pavlyuchenkova made the last 16 of a Slam for the first time since the 2011 US Open by seeing off Swiss 11th seed Timea Bacsinszky 6-3, 6-2.
Pavlyuchenkova will face US 27th seed Coco Vandeweghe, who knocked out sixth-seeded Italian Roberta Vinci 6-3, 6-4.
Vandeweghe is one of the in-form players on grass this year, winning at ‘s-Hertogenbosch and making the semi-finals in Birmingham.
Russia’s Elena Vesnina made the fourth round for the first time in seven years by ending the run of US qualifier Julia Boserup, the world number 225, in straight sets, 7-5, 7-5.
Vesnina will face doubles partner and close friend Ekaterina Makarova, who was a bridesmaid at her wedding last year, for a spot in the quarter-finals.
French 32nd seed Lucas Pouille saw off former US Open champion Juan Martin del Potro 6-7 (7/4), 7-6 (8/6), 7-5, 6-1 in a tie held over from Saturday.
Pouille next faces Australian 19th seed Bernard Tomic in what will be his first appearance in the last 16 at a major.