PARIS – After 20-year-old Garbiñe Muguruza upset top-ranked Serena Williams on Wednesday, she said “now is the moment” for the next generation in women’s tennis.

Ajla Tomljanovic, a 21-year-old Croat, provided yet another answer to that clarion call Friday, knocking out No. 3 Agnieszka Radwanska of Poland in the third round, 6-4, 6-4.

On Tuesday, the second-seeded player, Li Na of China, lost to 21-year-old Kristina Mladenovic, so the top three seeds are out of the women’s draw before the fourth round — the first time in the Open era that has happened at a Grand Slam event.

Fifth-ranked Victoria Azarenka of Belarus is not playing here because of an injury, creating a wide-open tournament seemingly ready to be seized.

Radwanska, seeking her first major title, did not seize it. She has never had much success at the French Open, her best result on the red clay at Roland Garros being a quarterfinal appearance last year. She quickly fell behind 5-1 in the first set, her normal bag of tricks rendered futile by her own errors and Tomljanovic’s aggressiveness.

After she was broken to open the second set, Radwanska got three break-point opportunities in the eighth game of the set, wasting them all.

“It doesn’t mean if first and second seed lost, doesn’t mean the third one is going to win,” said Radwanska, adding, “I just didn’t play good enough today to win the match.”

The 72nd-ranked Tomljanovic is having a tournament full of firsts. This is her first appearance in the main draw at the French Open. It is also the first time she has advanced past the second round at a major event. The victory Friday was her first over a top-25 player.

She joked that her postmatch news conference was the first time she was in front of so many lights.

But the success of her peers against top seeds gave her confidence going into the match.

“After seeing the two first seeds go out, you kind of feel like, ‘I can do this, too,’ ” Tomljanovic said. “I grew up with these girls that are beating them.”

Note

• Second-seeded Novak Djokovic of Serbia and No. 4 Roger Federer of Switzerland both needed four sets to reach the fourth round.

Djokovic beat No. 25 Marin Cilic of Croatia 6-3, 6-2, 6-7 (2-7), 6-4, improving to 9-0 in their head-to-head meetings.

Federer wasted four set points in the second set on his way to a 7-5, 6-7 (7-9), 6-2, 6-4 victory over No. 31 Dmitry Tursunov of Russia.