Serena Williams continued her quest for a record-equalling 24th Grand Slam title by reaching the French Open second week for the first time since 2018, after third seed Aryna Sabalenka's surprise loss left the veteran American as the highest-ranked player in her half of the draw.

In the men's third round, fifth seed Stefanos Tsitsipas and Daniil Medvedev beat big-serving Americans in John Isner and Reilly Opelka respectively.

Three-time Roland Garros champion Williams came through a potentially tricky third-round tie with compatriot Danielle Collins, winning 6-4, 6-4.

Zverev will face Nishikori in the fourth round Zverev will face Nishikori in the fourth round Photo: AFP / Christophe ARCHAMBAULT

She will next face Kazakh 21st seed Elena Rybakina, with a possible quarter-final against old rival Victoria Azarenka up for grabs.

The 39-year-old Williams, still one short of Margaret Court's all-time record of most Grand Slam singles titles, thundered down five aces and struck 22 winners past Collins.

"Today it was very difficult, but I played well, stayed concentrated. I'm very happy," said Williams, who fought back from 1-4 down in the second set.

The eighth seed had already seen yet another of her potential title rivals exit the tournament on Thursday, when world number one Ashleigh Barty hobbled out during the second round with a hip injury.

Sabalenka failed to improve her poor Grand Slam form on Friday Sabalenka failed to improve her poor Grand Slam form on Friday Photo: AFP / MARTIN BUREAU

After Naomi Osaka's shock withdrawal, Simona Halep failing to start the tournament through injury and early losses for Bianca Andreescu and Angelique Kerber, none of the players who have beaten Williams in Grand Slam finals since her last title in the 2017 Australian Open are still in the competition.

World number four Sabalenka, who was the highest-seeded women's player still in the tournament at the start of the day, was dumped out by Russia's Anastasia Pavlyuchenkova.

The Belarusian, who has never reached a Grand Slam quarter-final, slumped to a 6-4, 2-6, 6-0 defeat.

Serena Williams is still chasing a record-equalling 24th major Serena Williams is still chasing a record-equalling 24th major Photo: AFP / Christophe ARCHAMBAULT

The 31st-seeded Pavlyuchenkova will next face Azarenka.

Former world number one Azarenka, who stunned Williams in their 23rd meeting in last year's US Open semi-finals, cruised past Madison Keys 6-2, 6-2 to reach the Roland Garros fourth round for the first time since making the last four in 2013.

Three wins in a row: Medvedev had lost eight of nine clay-court matches before this tournament Three wins in a row: Medvedev had lost eight of nine clay-court matches before this tournament Photo: AFP / Anne-Christine POUJOULAT

Men's fifth seed Tsitsipas came through the most serious test of his title credentials so far with a hard-fought victory over Isner in four sets in the night match.

The 22-year-old Greek, who lost a dramatic semi-final last year to Novak Djokovic, bounced back from losing a tight first set to win 5-7, 6-3, 7-6 (7/3), 6-1.

An excellent third-set tie-break was the key to securing a fourth-round match against Spanish 12th seed Pablo Carreno Busta, who eased past Steve Johnson 6-4, 6-4, 6-2.

"I didn't have the best start I would say, but things started going my way in the second set. My head kind of cleared up and helped me to that important victory," said Tsitsipas whose win ended US men's hopes in the tournament.

Second seed Medvedev was adopted as the new home favourite by the French crowd as he eased to a straight-sets win over Opelka on Court Suzanne Lenglen.

The two-time Grand Slam runner-up, who speaks French and lived in France as a youngster, impressed in a 6-4, 6-2, 6-4 success.

Medvedev had lost all four of his previous French Open matches before this week, but received generous support from the fans, with no French players in the third round for the first time in the Open era.

The Russian will face Cristian Garin for a last-eight spot after the Chilean beat US player Marcos Giron 6-1, 5-7, 6-2, 6-2.

German sixth seed Alexander Zverev needed five sets to beat unheralded compatriot Oscar Otte in the first round before edging Russian qualifier Roman Safiullin in three tight sets.

He cruised to a 6-2, 7-5, 6-2 win over Laslo Djere on Friday, though, setting up a last-16 clash with former world number four Kei Nishikori.

"This is the main goal of my tennis career, to win Grand Slams, to reach the top of the rankings. I feel like the last year I'm on the right track again," said Zverev.

Nishikori reached the fourth round when opponent Henri Laaksonen retired injured after dropping the first set.

The short outing would have been a relief for Japan's Nishikori, who spent more than eight hours on court over the first two rounds.

In-form Norwegian youngster Casper Ruud was knocked out by Alejandro Davidovich Fokina in a marathon match which lasted more than four-and-a-half hours.

The Spaniard clinched victory in a dramatic final game, even including an underarm serve, on his fifth match point, winning 7-6 (7/3), 2-6, 7-6 (8/6), 0-6, 7-5 to secure a last-16 date with Argentina's Federico Delbonis.