PARIS (REUTERS) - Petra Kvitova required all her firepower to subdue Canadian teenager Leylah Fernandez as she overcame a terrible start to win 7-5 6-3 and reach the French Open fourth round on Saturday.

The 30-year-old Czech struck 32 winners and needed every one of them to halt her young opponent's dream debut.

Kvitova was caught cold on a clammy Court Suzanne Lenglen as she trailed 5-1 in the opening set against last year's French Open junior champion who played beautifully early on.

Kvitova had to save a set point at 1-5 and another at 3-5 before her power game really began to have an impact.

She won nine games in a row to take charge but the 5ft 4ins Fernandez, the youngest player left in the draw, never looked flustered as she continued asking questions of her fellow left-hander with clever shot-making.

Fernandez recovered one break of serve in the second set and, with Kvitova showing signs of anxiety, had two more break points to level the set at 4-4 but Kvitova held firm to move 5-3 ahead with a superbly-angled volley.

There was a fair amount of relief in Kvitova's expression as she hammered a winner for victory, offering some warm words to her opponent at the net.

Twice Wimbledon champion Kvitova has reached the fourth round in Paris for the fifth time and will be starting to fancy her chances with China's unseeded Shuai Zhang up next.