Fresh off of a run to the US Open final, world number 14 Azarenka hit 22 winners and converted six of 14 break points to pick up just her third victory in nine career meetings against the seven-time major champion.
Azarenka stays hot, dispatches Venus to advance
The Belarusian, who has now won 12 of her last 13 matches, was first to strike, breaking Williams in a nine-minute game to take a 2-0 lead and she consolidated her advantage with a love hold, capped by an ace to make it 3-0.
The American was quick to respond, breaking back in the fifth game and leveling the set by winning her third straight game, also holding by way of an ace. Azarenka responded with some fierce returning to break for a second time and move in front 5-3.
Once again Williams would respond, breaking to stay in the set and saving a set point with a big serve down the middle to make the score 5-5. She took her first lead of the match after slamming a backhand winner down the line to break only to see Azarenka break back and force a tiebreaker.
In the breaker, Azarenka rifled off consecutive winners to seemingly break it open, going ahead 5-2. Once again, Williams roared back and an error from the Belarusian gave her a set point at 6-5. At 7-7, Williams committed back-to-back forehand errors to cede a tight opening set to the two-time major champion.
The second set was not as close, Azarenka rallying from 40-15 down to break after a Williams double fault. She jumped ahead 4-1 after a second break and despite an exchange of breaks, she came through a 0-30 deficit thanks to four straight errors by the American to clinch a spot in the second round.