Montreal, Aug 14 (DPA) Roger Federer and Rafael Nadal resumed their dominance in tennis, with the top two seeds powering into the quarter-finals of the Montreal Masters.

Number one Federer defeated countryman and good friend Stan Wawrinka 6-3, 7-6(5), while Nadal, making a comeback from a knee injury, eased his mind with a second victory in 24 hours, defeating German Philipp Petzschner 6-3, 6-2 here Thursday.

Federer missed on four match points in the second-set tiebreaker, with Wawrinka ultimately getting a low volley at the net wrong to lose in just under two hours.

'It was a tense match, you can never tell until it's over,' said Federer, who has won his last three tournaments. 'Stan was serving really well. We played at a high level.'

'It was a very equal match,' said Federer, 42-6 on the season. 'Stan had chances and played very well. But I served well when I needed to. I'm pleased to get through.'

Federer next plays France's Jo-Wilfried Tsonga, a winner over Gilles Simon 6-3, 6-3.

It was all but effortless for Nadal, who last played May 31.

'I said before the tournament that my goal here is only try to improve every day,' said Nadal, the four-time French Open champion. 'I think that's what I'm doing. I'm very happy to be in the quarter-finals, it's more than what I expected.