Serena Williams is asked about former rival who's now a coach

PARIS — On Monday at the French Open, Serena Williams will face an old foe, but with one caveat: Her one-time nemesis will be in her opponent’s corner, not across the net from her.

Set to play 21-year-old Elina Svitolina, a Ukrainian, Williams will also go against bygone rival Justine Henin, who Svitolina has brought on as an adviser.

Can Henin, a former world No. 1, give Svitolina an edge? She was 2-0 against Williams at the French Open, including an infamous 2003 semifinal.

“It really doesn't matter,” Serena said Saturday of Henin’s advising role to Svitolina. “It's just really about going out there and playing your best. That's really all I can do right now. That's all I look forward to doing.”

Serena is joined by older sister Venus in the fourth round of the French Open for the first time since 2010. Four American women — Madison Keys and Shelby Rogers, as well — are into the round of 16 here for just the second time here in 12 years.

Caroline Wozniacki wants to play in Olympics, but she must appeal

At 35, Venus continues to play aggressive, first-strike tennis, a game that doesn’t always translate on the slow red clay of Paris. She’ll be challenged by a crafty and creative Swiss player, Timea Bacsinszky, who Serena needed three sets to beat in the semifinals in 2015.

“The life of a tennis player is a long one,” Venus told reporters. “You just try to get better. I've just tried to get better, to sum it up. On all counts.”

Saturday evening, after they both won singles matches on main stadiums, Venus and Serena played doubles on a half-full Court 3, tucked in the corner of the Roland Garros tournament site.

The sisters won the first set over Vitalia Diatchenko and Galina Voskoboeva 7-6(8), but then the match was suspended due to fading light. They’ll resume on Sunday and – should they win – have to play a second doubles match later in the day.

Venus and Serena have spent much of their careers side by side, and this fortnight is no different, but their presence for one another is comforting – motivating almost. Both would need to win two more matches for them to face off in the semifinals.

“It's nice,” a smiling Venus said. “We always support each other. It's nice to be able to spend time together.”

Then she added: “I watch a lot of Food Network shows. Serena loves it, the Food Network. So we end up watching a lot of I don't know what ...”

Svitolina is a spitfire on court, sometimes even hot-tempered. She took a set off Serena at the 2015 Australian Open and has maintained her coach in Iain Hughes as Henin, a former world No. 1 who retired (for a second time) in 2011, is tasked with the helping her become a stronger thinker on court.

“She understands what I feel… she has been out on court,” Svitolina said of Henin. “Because for some coaches who didn't play on such a high level, it's tough. It's just different. It's not bad; it's not good. She's more on the mental side of things for me.”

Serena Williams and Henin, 33, have never had a warm relationship, and it turned particularly frosty after the 2003 semifinal when Williams felt as though Henin had acted unfairly in a tense third set. Henin won her first French Open that year, and three more to follow.

“I didn't even realize she was coaching,” Serena said earlier this tournament about Henin, who is a year her junior. “I was like, ‘Gosh, it's a little bit surreal.’”

PHOTOS: BEST OF THE FRENCH OPEN