Defending champion Naomi Osaka has overcome a mid-match wobble to advance to the third round of the Australian Open with a straight-sets win over China’s Zheng Saisai.

The world No.4 became frustrated during her 6-2 6-4 victory on Margaret Court Arena, with windy conditions forcing her to hit a number of balls long.

After cruising through the first set, the Japanese third seed was broken twice early in the second, but won the last four games after being down 4-2.

“I got really fired when she (Zheng) was up 4-2 and people started clapping more … for the drama,” Osaka said post-match.

“I was complaining over here and almost throwing my racquet over there, but it worked out.

“I know I’ve been in this position on this court before, but I really didn’t want to play a third set this time.”

Osaka’s triumph sets up a potential third-round showdown with American teen sensation Coco Gauff.

Fifteen-year-old Gauff plays Romania’s Sorana Cirstea later on Wednesday.

The woman Osaka defeated in last year’s final, Petra Kvitova, also won her second round match after a tough straight-sets victory over Spain’s Paula Badosa.

After dropping just one game during her first round blitz, the Czech seventh seed was made to work harder this time, but still did enough to prevail 7-5 7-5.

World No.97 Badosa celebrated when she was convinced she had taken the second set on Rod Laver Arena after leading 5-4, but her winner cruelly dropped just wide.

Kvitova then responded to hold her serve and win the final three games of the match.

“She (Badosa) played a great match and made it really tough for me to get through,” Kvitova said post-match.

“The wind was not really nice. (Badosa) is a talented player and she will be a very good player in the future.”

But 11th seed Aryna Sabalenka and 13th seed Petra Martic tumbled out in eartly boilovers on Wednesday.

Tipped as an Open dark horse, Sabalenka lost 7-6 (8-6) 7-6 (8-6) to veteran Spaniard Carla Suarez Navarro, a three-time Melbourne Park quarter-finalist.

Martic lost to German Julia Goerges 4-6 6-3 7-5.

American Alison Riske is on track for a round of 16 blockbuster with Ashleigh Barty after the 18th seed annihilated China’s Zhu Lin 6-3 6-1 in the second round.

Australian wildcard Astra Sharma lost her delayed first-round match after going down to Estonian 28th seed Anett Kontaviet 6-0 6-2.