* Azarenka committed nine double faults in victory
* Will play Daniela Hantuchova in quarter-finals (Adds quotes)
By Julian Linden
NEW YORK, Sept 3 (Reuters) - Victoria Azarenka booked her place in the quarter-finals of the U.S. Open on Tuesday when she beat Serbia's Ana Ivanovic 4-6 6-3 6-4 in an error-strewn fourth-round match.
Azarenka dropped her opening set for the second match in a row but fought her way back to win after more than two gruelling hours on a windy Arthur Ashe Stadium.
"Ana just came out firing, she played amazing tennis in the first set ... ripping winners and serving great," Azarenka said.
"I really had to wake up in the second set."
The Belarussian's next opponent is unseeded Slovakian Daniela Hantuchova, who beat American wildcard Alison Riske on Monday to reach her first quarter-final at Flushing Meadows in over a decade.
Azarenka's round of 16 clash with Ivanovic was also meant to be played on Monday but was postponed until Tuesday after a five-hour rain delay forced tournament organisers to cancel dozens of matches.
Conditions at the U.S. National Tennis Center were not much better on Tuesday with Azarenka and Ivanovic both struggling with their serves in the gusting winds.
World number two Azarenka had her serve broken seven times and committed nine double faults, while Ivanovic lost nine of her service games and made eight doubles after making a flying start.
"I really played well. I put her a lot under pressure, I felt," said Ivanovic. "I think the biggest difference was the serve in the second set. My percentage went right down.
"I felt like I could break her, but it was very frustrating that I was losing my serve constantly."
The match was still in the balance with the players locked at 3-3 in the deciding set when Azarenka, who made the U.S. Open final last year, seized control.
She held her own service game then broke Ivanovic again when the former world number one sent a backhand wide.
She squandered two match points on her own serve before a desperate Ivanovic broke back but closed out the match in the following game on her fourth match point when the Serbian dumped a backhand into the net.
"I take whatever I have," Azarenka said.
"If I have to fight and dig deep to find a way, not playing at your best against a player who was playing that good, I think it's pretty remarkable to walk off the court with a win."
Although Azarenka has not been at her best so far in the tournament, many experts are still tipping her to make the final and possibly earn a rematch with Serena Williams.
Azarenka was two points away from upsetting Williams in last year's final and recently beat the American in Cincinnati, one of the key warm-up events for the last grand slam of the season.
"I'm a fighter at heart. I never, never give up," Azarenka said. "Whatever the score is, I'm going to try to do my best because there is always an opportunity. There is always a way." (Editing by Frank Pingue)