MELBOURNE — Serena Williams overcame a spirited Nina Stojanović (6-3, 6-0) on a sun-drenched Rod Laver Arena to reach the third round of the Australian Open for the 19th time on Wednesday.

The American, again sporting her distinctive one-legged leotard, needed to find her best game at times in the first set against a Serbian 15 years her junior who was playing in her fourth Grand Slam.

Ms. Williams has won seven major titles at Melbourne Park alone, of course, and ramped up her serve to see off the danger before putting the pressure back on her opponent with some booming service returns.

“She pushed me really hard and played well throughout the match,” the 39-year-old said.

The second set was one-way traffic and Ms. Williams fired down her sixth ace of the contest to seal a date with Anastasia Potapova, taking another step on the path she hopes will end with a record-equalling 24th Grand Slam title.

Two-time Wimbledon champion Petra Kvitova was sent packing from the Australian Open on Wednesday after a (6-4, 1-6, 6-1) second-round defeat by Romanian Sorana Cîrstea.

Ms. Kvitova jumped out to a 2-0 lead but could not keep a lid on her errors as Ms. Cîrstea converted each of her three breakpoint opportunities to claim the opening set.

Ms. Kvitova, who finished runner-up at Melbourne Park two years ago, showed glimpses of her powerful ball-striking as she raced to a 4-0 lead in the second set before levelling the match when Ms. Cîrstea handed her a third break with a tame double fault.

Ms. Cîrstea, however, turned the tables on the Czech in the final set and claimed victory on her third match point with Ms. Kvitova hitting a forehand long. — Reuters