Serena Williams sent out a warning to the rest of the depleted women's draw on Friday with a dominant straight-sets win over Danielle Collins to reach the French Open last 16 for the first time since 2018.

The 39-year-old, still one short of Margaret Court's all-time record of 24 Grand Slam singles titles, saw off fellow American Collins 6-4, 6-4, fighting back from 1-4 down in the second set.

"I needed to win being down. I needed to find me, know who I am," said Williams, who had only won one of three clay-court matches this year before the tournament.

"Nobody else is Serena out here. It's me. It's pretty cool."

Williams is now the highest seed left in her half of the draw, with all of the world's top four absent from the second week.

"There's still a lot of matches, a lot of great players, as we can see," she added.

"There's so much depth in this game now, it doesn't matter if you're playing in the first round or not, you really have to fight for every match and nothing comes easy."

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

The 21-year-old Rybakina described her fourth-round opponent as "the legend of the sport" after beating Elena Vesnina on Friday.

"It's an interesting position to be in because I've been in that position, too, where I've played people that I really admired, but at the same time I wanted to win the match," said Williams.

"The tables are turned. So now, I feel like that's the same situation, but they want to win.

"Then they have nothing to lose. They just are hitting lines. You have to just realise that you can hit the lines, too."

Williams, seeded eighth, had a slight scare in the second set when she fell a break down to 2020 quarter-finalist Collins, but won the next five games to secure victory.

When Williams last made the fourth round three years ago, she withdrew injured before a scheduled clash with Maria Sharapova.

The former world number one also pulled out last year following the opening round, but she looks in strong form this time around, despite sporting some strapping on her right thigh.

Williams thundered down five aces and hit 22 winners against Collins, winning in just 85 minutes on Court Philippe Chatrier.