ST PETERSBURG (REUTERS) - Top seed Petra Kvitova shook off her Australian Open hangover to beat Belarusian Victoria Azarenka 6-2 7-6(3) in the St Petersburg Ladies Trophy on Wednesday (Jan 30), but not before the former world number one gave the Czech a scare.

Kvitova, the defending champion, showed she was still feeling the effects of Saturday's defeat by Naomi Osaka in the Australian Open final as she lost her first two service games.

The world number two managed to break back immediately on both occasions before holding for the first time, and then used her powerful groundstrokes to dominate the longer rallies and claim the opener.

With her serve firing, Kvitova charged out of the blocks in the second set, winning the first three games to spark what looked to be a stroll into the quarter-finals and breaking Azarenka's serve again to open up a 5-1 lead.

But the Czech double faulted on match point, allowing Azarenka to break back and mount what was almost a fightback for the ages.

"I don't know why (the double fault) happened. I really wanted to finish it earlier but unfortunately I had to fight in the second set and I did quite well in the tiebreak," Kvitova said courtside after her win.

Azarenka, her confidence restored, pinned Kvitova back behind the baseline with her aggressive tennis, and broke again to level the set at 5-5 and force a tiebreak.

Kvitova hit 40 winners to Azarenka's 14, but she also made 33 unforced errors compared with 17 from her opponent.

The Czech's composure came to the fore in the tiebreak and she closed out the match with a powerful backhand down the line to set up a quarter-final clash with either Russia's Veronika Kudermetova or Croatia's Donna Vekic.