Serena Williams overcame a spirited Nina Stojanovic 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, while two-time Wimbledon champion Petra Kvitova was sent packing after a 6-4 1-6 6-1 defeat by Romanian Sorana Cirstea.

Williams, 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.

The American 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.

"I wasn't thinking so much in the second set."

The second set was one-way traffic and 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.

-Cirstea sends Kvitova crashing out -

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

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 Cirstea handed her a third break with a tame double fault.

Sorana Cirstea celebrates after beating Petra Kvitova.   -  GETTY IMAGES

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

"I was one of the few in hard quarantine. I think it's impressive to come out of 15 days without hitting a ball and competing the way I did today, I wasn't expecting it," said Cirstea, who will next face Czech Marketa Vondrousova.