Sidelined for more than two months with tendonitis in both knees, Nadal could not hide his delight at being back on centre court, the muscular Mallorcan bounding and dancing around Stade Uniprix to wild applause after his 66-minute workout.
"A little better, the movement was a little better," the defending champion told reporters. "I am happy because I am in the quarter-finals and it is more than I expected when I came here.
"The feeling is much better than what I thought when I was on the plane coming to Montreal."
Nadal eased his way back into action on the Canadian hardcourts with a pair of doubles matches and had been looking forward to his first serious test on Wednesday with a second round clash against Davis Cup team mate David Ferrer.
But Nadal learned little about his fitness from that match after Ferrer was forced to retire when trailing 4-3 in the opening set because of a sore knee.
The Spaniard's third round match against the 45th-ranked Petzschner was much more revealing, however, the world number two quickly finding his rhythm and his physical, attacking style of play.
Nadal will face a much sterner test in the quarter-finals against sixth seed Argentine Juan Martin Del Potro, who is in superb hardcourt form after winning the Washington Classic last week.
"My goal here is only to try to improve," said Nadal. "I know tomorrow I am not the favourite for sure.
"He [won] in Washington and won today a very tough match, so he is coming with big confidence."