Nadal showed inevitable signs of rustiness as he battled past Wawrinka
Rafael Nadal came through a testing encounter at the Rogers Cup in Toronto in his first match since Wimbledon.
The world number one needed two hours and 20 minutes to see off Stanislas Wawrinka 7-6 (14-12) 6-3.
Their epic first-set tie-break match was the longest of Nadal's career, but the Spaniard was happy with his return.
"I had difficult moments, I had moments where I played well, I did a little bit of everything. I just tried my best and tried to find my rhythm," he said.
Nadal drew on all his experience and trademark refusal to give in as he outlasted Wawrinka in an opening set that lasted a gruelling 92 minutes.
In previous five meetings, the Swiss world number 24 had never taken a set off the Spaniard, never mind a victory.
Nadal next faces South Africa's Kevin Anderson who beat American 16th seed Sam Querrey 7-6 (7-4) 4-6, 6-4.
Earlier, world number two Novak Djokovic was forced to dig even deeper as he defeated France's Julien Benneteau 7-5 7-5 in sweltering midday conditions.
I have said before, I will never risk my health to win and I was really on the edge
A winner in Canada in 2007, Djokovic appeared uncomfortable the moment he stepped onto the court and summoned a trainer after going down a break in the second set.
His two-hour victory left the Serb drained, slumped over the net gasping for breath.
"I have said before, I will never risk my health to win and I was really on the edge," said Djokovic, who has struggled with heat-related issues throughout his career.
"If your body gives you signs that something bad is going on you have to do something... no-one can turn off the sun, even though I would like it."
In other second-round matches, Russian sixth seed Nikolay Davydenko had a 7-5 6-1 win over Italian Fabio Fognini, while Jeremy Chardy of France upset ninth-seeded Fernando Verdasco of Spain 6-7 (5-7) 7-6 (7-5) 6-2.
Ukraine's Alexandr Dolgopolov ousted 12th Mikhail Youzhny 1-6 7-6 (7-4) 7-5, and Frenchman Michael Llodra beat 14th seed Nicolas Almagro of Spain 7-6 (7-5) 6-2.
David Nalbandian, who won the Legg Mason Classic in Washington on Sunday, continued his good run of form with a 6-3 6-0 win over Spain's Tommy Robredo.
The Argentine only returned to competitive action last week after a long lay-off following hip surgery and then hamstring problems.