Sept. 29 (UPI) -- Serena Williams, Rafael Nadal, Dominic Thiem and Elina Svitolina all advanced while Daniil Medvedev, Gael Monfils and Madison Keys were upset in the opening round of the 2020 French Open Monday -- which is being staged four months later than usual this year.
"I just need to play with more confidence, like I'm Serena," Williams told reporters. "I just started playing like that. I was moving and sliding and I think her level dropped a little bit after the first set.
"I took advantage of that."
The 23-time Grand Slam champion hit 11 aces and 26 winners in the one-hour, 41-minute match.
Williams won the first point of the first set before Ahn rallied for a 3-1 lead. They traded the next two points before Ahn broke Williams' serve to win the ninth game. Williams won the next two games for a 6-5 lead before Ahn forced a tiebreak, which Williams won to take the first set.
Ahn wouldn't win another game. Williams dominated the second set and clinched the victory with a 101-mph ace at match point.
Svitolina -- the No. 3 seed -- was the highest-seeded player to advance Monday from the women's singles draw, beating Varvara Gracheva in straight sets.
No. 5 Kiki Bertens beat Katarina Zavatska in three sets and No. 7 Petra Kvitova beat Oceane Dodin without losing a set. Unseeded Zhang Shuai bounced Keys -- the No. 12 seed -- in straight sets.
Nadal -- the No. 2 seed in the men's singles draw -- beat Egor Gerasimov 6-4, 6-4, 6-2, and was the highest-seeded men's player to advance Monday. The 12-time French Open champion hit three aces, 32 winners and 20 unforced errors in the win. Gerasimov committed 28 errors in the two-hour, five-minute match.
Nadal, who next faces American Mackenzie McDonald in the second round Wednesday, hopes to win the French Open for a fourth consecutive time.
"That was a normal first match for Roland Garros," Nadal said. "I am happy. I did the things I had to do. I didn't expect much more.
"I did things well and I am happy for the victory."
Thiem, the No. 3 seed, defeated Croat and former U.S. Open champion Marin Cilic in straight sets. Italian Marton Fucsovics ousted Medvedev, the No. 4 seed, with a 6-4, 7-6 (3), 2-6, 6-1 triumph. Medvedev came unraveled with 51 unforced errors in the three-hour, 17-minute match.
Monfils, the No. 8 seed, fell to unseeded Alexander Bublik, who hit six aces and 47 winners in the two-hour, 35-minute match. Monfils committed 58 errors and 12 double faults.
Tuesday's French Open slate features No. 1 Novak Djokovic, No. 5 Stefanos Tsitsipas, No. 9 Denis Shapovalov and No. 10 Roberto Bautista Agut on the men's side -- and No. 2 Karolína Plíšková, fourth-seeded American Sofia Kenin and No. 8 Aryna Sabalenka in the women's draw.