“Are you freaking kidding me?” Azarenka howled to the chair umpire.
“What the hell are you doing?” she asked.
After the match, she put it this way: “That was the most ridiculous thing there is.”
On her second try at set point, Azarenka hit a forehand wide to send the game to deuce, but she won the next two points to clinch the set.
Then she dominated the third to advance to face 13th seed Ana Ivanovic, who beat young American Christina McHale 4-6, 7-5, 6-4 in 2 hours, 26 minutes.
McHale served for the match at 5-4 in the second set and also had two break points at 5-5.
While McHale lost, another young American, Alison Riske, pulled off an impressive scalp by cruising past former Wimbledon champion Petra Kvitova 6-3, 6-0.
The Czech had been in bed with a fever the day before.
“My body wouldn’t let me fight,” Kvitova said.
Simona Halep, seeded 21st, crushed No. 14 Maria Kirilenko 6-1, 6-0, setting up a clash with Flavia Pennetta, who beat 27th seed Svetlana Kuznetsova 7-5, 6-1.
No. 10 Roberta Vinci will face unseeded Camila Giorgi in an all-Italian match.
The 136th-ranked Giorgi defeated 2009 US Open runner-up Caroline Wozniacki, who was seeded sixth, 4-6, 6-4, 6-3.