MONTREAL (Reuters) - Petra Kvitova overcame a mid-match slump to claim her first title of the season with a 7-5 2-6 6-3 victory over China's Li Na in the Montreal Cup on Monday.

In an entertaining but erratic encounter between two former major winners, the fifth-seed's first tournament win since last October's WTA Championship will lift the Czech's confidence ahead of the U.S. Open starting at the end of the month.

The 22-year-old's maiden victory on North American soil pocketed last year's Wimbledon champion $385,000 but it was not without drama.

The momentum shifted several times during the match but none more evidently than when Li won the first 16 points of the second set to race into a 4-0 lead after the 30-year-old 10th seed had dropped the opener.

Li, who remains without a title in 2012 after losing finals in Sydney, Rome and now Montreal, had started well before Kvitova eked out a 5-3 lead.

The 2011 French Open champion, who will return to the top 10 in the world rankings, fought back to level at 5-5 but was unable to covert a further four break points before suffering a bout of nerves on her next service game to drop the set.

Li responded immediately, aided by some wayward play from her opponent, winning the first four games of the second set without dropping a point as Kvitova lost focus and struggled to land in the ball in the court.

That Kvitova made 16 unforced errors while hitting just one winner indicated just how off-target the Czech had become during the second set.

However, the 22-year-old Czech regrouped at the start of the third and regained the advantage when Li overhit a forehand while trailing 2-3 to drop serve and Kvitova held her nerve to seal a much-needed victory.

(Editing by John O'Brien)