Raonic fought off a match point and the injury in the third set to pull out a five-set victory over Serbia's Janko Tipsarevic to tie the best-of-five Davis Cup semifinal at one match apiece.
The 22-year-old from Thornhill, Ont., leaned heavily on his booming serve to avoid testing his taped ankle.
"I felt like playing aggressively was the key. I started serving in the fourth (set) on and starting going for it more," said Raonic. "That helped me survive a lot of tough issues and then just kept plugging away."
Raonic needed four hours 12 minutes to complete the 5-7, 6-3, 3-6, 6-3, 10-8 victory at the Belgrade Arena. Earlier, top-ranked Novak Djokovic had little trouble in a 6-2, 6-0, 6-4 win over Vancouver's Vasek Pospisil.
Of his 34 aces served up in the match, Raonic hit 17 in the fifth set alone.
Raonic appeared to roll over on his ankle near the end of the third set but didn't receive treatment until the changeover to the fourth set. He got the ankle taped before going out to take the fourth set on the strength of seven more aces.
He didn't know the extent of the problem but said he only noticed it on certain movements.
After leaving the arena, Raonic was to receive some treatment and was adamant that he'll be ready for his reverse singles match against Djokovic that kicks off the action on Sunday.
"I won't think too much of it until I get more information," said Raonic. "It's just a waste of energy until I actually know what's actually happening."
Heading into the fifth set there was another longer changeover when the referee called for the clay court to be watered. As a result, the fifth set started with the court still damp.
It's always the referee who has discretion in such matters but Raonic didn't like how the situation was handled.
"I don't think the issue is with it being watered, I think the issue is with how the head referee dealt with it," said Raonic. "I found it very unprofessional without consulting once and just I don't think he did a good job dealing with that situation.
"It's disappointing because I'm sure he's been in that situation many times."
The victory takes some of the pressure off Pospisil and Toronto's Daniel Nestor, who will team up in Saturday's doubles match against Ilija Bozoljac and Nenad Zimonic. A Raonic loss would have created a must-win situation for the Canadian doubles duo.
Reverse singles matches are on tap for Sunday. The singles draws are flipped with Djokovic to open against Raonic and Tipsarevic to play Pospisil.
The winner of the tie will play either the Czech Republic or Argentina in the final in November. The Czechs won both singles matches Friday for a 2-0 lead.
Djokovic, who was coming off a loss to Rafael Nadal in the U.S. Open final on Monday, won 12 consecutive games midway through the opening match. He completed the victory in one hour 41 minutes.
"I'm not going to put up any excuses. He's the No. 1 in the world for a reason and I thought he played amazing," said Pospisil. "He didn't make any mistakes. I have to play my best tennis to keep it close and I was playing well in the beginning and after I went down a break I started panicking a bit and wasn't playing my best."
Pospisil has had a breakthrough season and is up to No. 41 in the world rankings. However, he was unable to put much pressure on Djokovic and committed 75 unforced errors.
There was a small pocket of Canadian fans in the 15,000-seat venue and they were in full voice early as Pospisil easily held serve in the opening game. Pospisil had his serve broken in the fifth game and Djokovic took control.
Djokovic appeared fresh despite a busy travel week and limited practice time. He needed only 28 minutes to win the second set.
"I was forcing it too much and I wasn't in my own skin," said Pospisil. "He makes you do that by just being Novak and playing the way he was playing, he maybe forced me to go for a little too much and there was probably a 45-minute period where it probably wasn't too pretty for my side."
Pospisil played better in the third set despite being broken in the first game. He held serve the rest of the way but Djokovic was steady and secured the win when Pospisil put a shot into the net.
Canada, which upset Spain and Italy in Vancouver to advance, has never reached the Davis Cup semifinals in the modern era. Serbia, meanwhile, is trying to get back to the final after winning the event in 2010.