* Second seed overcomes sub-par play
* Azarenka faces Ivanovic in next round (Adds quotes)
By Julian Linden
NEW YORK, Aug 31 (Reuters) - A feisty Victoria Azarenka dropped her first set of the tournament on Saturday before regaining her composure to safely book her place in the last 16 at the U.S. Open.
A finalist last year and one of the favourites to win the title this season, the Belarussian passed her first real test at the championship in beating beat Alize Cornet of France 6-7(2) 6-3 6-2.
By her own admission, this was not one of Azarenka's best performances. She made 38 unforced errors and got involved in an argument with the chair umpire over a line call.
"I don't think I played my best tennis today but I have to give her credit. She played really well," Azarenka said.
"The dynamic of the match was a little bit weird for me.
"I felt like I didn't take my opportunities in the first set, which was kind of a waste and it gave her a lot of confidence."
The first set took more than an hour to complete and the 24-year-old Azarenka was frustrated that she let it go after fighting back from 4-1 behind to force a tiebreak.
But she raised her game in the remaining two sets, reducing her unforced error count.
"That was more me playing, more finding the rhythm," she said.
"I felt much better in the third set than in the first set which was going past the two-hour mark. It's pretty good, so I'm happy with that."
Azarenka's frustrations threatened to boil over when the umpire ordered a point she had won to be replayed and was still fuming about it after the match.
"That was the most ridiculous thing there is," she said.
"I had already walked to my chair, Alize almost walked to her chair, they said, 'replay the point'."
Despite her below-par performance, Azarenka said she enjoyed being under pressure, believing it brought out the best in her.
"I like pressure. I think pressure is something that if you want to be on top, you have to deal with," she said.
"That's what makes you better. You need that to be on top, to be motivated.
"If you don't have any pressure, if you don't feel like you have to achieve something, it's not fun. For me, I need that."
Azarenka's next opponent is former world number Ana Ivanovic, who also came from behind to win her center court clash with American Christina McHale 4-6 7-5 6-4.
"Ana is a great player," said Azarenka.
"She's definitely in great form, and I'm sure she's motivated and pumped up.
"It's going to be a good match. She's a great champion, as well. I'm looking forward to that." (Editing by Gene Cherry)