Closing the Rod Laver Arena roof and cranking up the air conditioning helped the defending champion pull herself together and advance to the semifinals -- but left her opponent steaming.
"I felt I was watching someone play in a blue dress, and it wasn't me, because it was so hot out there," said the second-ranked American, who beat Russia's Svetlana Kuznetsova 5-7, 7-5, 6-1. "And I kept trying to tell myself that it's not hot. But it got hotter."
Williams, seeking her fourth Australian title and 10th Grand Slam championship overall, next takes on Olympic gold medalist Elena Dementieva, who had to play her entire match with the roof open.
The fourth-seeded Dementieva ousted Carla Suarez Navarro 6-2, 6-2 to run her winning streak to 15 matches after she won two tune-up tournaments.
With temperatures soaring to 109 degrees on a cloudless day -- Williams had her rackets restrung during her match because they lost their tension -- the retractable roof was closed after Kuznestova won the first set.
The heat was beginning to take a toll on Williams, and the eighth-seeded Kuznetsova was angry at the decision. She felt that the break gave Williams time to recover and that playing indoors benefited the American's powerful serve.
"Why should I not be?" Kuznetsova said. "Game going my way. I was very comfortable playing outside. It's two different games. One you play inside; one you play outside. Serena was tough. She's playing great. I give her credit. But I don't get this rule."
Down a set and a break and with Kuznetsova serving for the match in the second set, Williams broke to get even at 5-5 when Kuznetsova missed an open-court volley that turned the match.
Williams held and again broke Kuznetsova's serve, forcing the deciding set. The American broke to lead 3-1 and, after saving two break points with a pair of forehand winners, the result was never in doubt.
Dementieva made a fast start against 20-year-old Suarez Navarro, of Spain, who upset Venus Williams in the second round, winning 16 of the first 18 points for a 4-0 lead.
She raced through the first five games in 22 minutes and, after eventually holding serve in a sixth game that went to deuce 11 times and lasted 17 minutes, finished off in 1 hour, 35 minutes.