The halt in proceedings came 63 minutes into the opening set, after Wawrinka saved a Nadal set point for 5-all, with the Spaniard then holding serve for 6-5.
A pair of Canadian teenagers advanced, with Denis Shapovalov dominating Jeremy Chardy 6-1, 6-4 while good friend Felix Auger-Aliassime, who turns 18 on Wednesday, thrilled his home fans as he defeated Lucas Pouille of France 6-4, 6-3.
Wawrinka, a three-time Grand Slam champion, came into the tournament ranked 195th in the world as he looks to get back into form following knee surgery.
"The main objective of the tweet was because I was disappointed, obviously not for myself, but because there was so many fans and friends that wanted to come watch me on centre court and they weren't able to", Shapovalov said.
It has happened for me, the big comeback, winning a big trophy in Wimbledon, in the best possible scenario in the best possible setting. You know, I'm going to be major in Montreal in Quebec.
Medvedev won 3-6, 6-4, 7-6 (9).
"I'm happy with the way I'm practicing".
"I need to earn my confidence on this surface and start it well to hopefully have a good tournament".
Kyrgios was at the centre of controversy in Canada three years ago when he alleged that fellow Australian Thanasi Kokkinakis had slept with Wawrinka's girlfriend, Donna Vekic.
Kyrgios, with green fluorescent tape encircling each kneecap, quit injured in last week's Washington quarter-finals, and he was treated in the second set here for his chronically troublesome hip. She won six straight games after the restart and needed only 36 minutes to win the second set.
Get breaking news alerts. That's why I called the trainer on the court.
"I think I played a solid match".
The 13-time Grand Slam title victor has now won 21 of his last 24 matches after a rollercoaster start to 2018 which saw him go 6-6.
Wawrinka has struggled this season following a second knee operation but the three-time major victor was back to his brilliant best against Nadal. "So that has changed and obviously feels good".
Novak Djokovic sent Peter Polansky of Canada to a 6-3, 6-4 defeat on Wednesday as the four-time champion powered into the third round at the Toronto Masters before insisting he s "comfortable" with the controversial shot clock innovation.
Also advancing to the third round were Wimbledon runner-up Kevin Anderson, fifth seed Grigor Dimitrov, sixth seed Marin Cilic, eighth seed John Isner, Dutchman Robin Haase and Russian Karen Khachanov, who upset Spanish 12th seed Pablo Carreno Busto 6-4 7-6 (3).