Duncan Robinson also had a big night for the Heat, finishing with 22 points on 8-of-11 shooting from the field and 6-of-9 shooting on threes.
It was a feel-good, relieving moment for the Raptors as Nurse announced that Lowry would be playing, and starting, in the game beforehand, followed by the welcome sight of Lowry's low-five-covered, workout-inspired player introduction just before tip-off.
Raptors head coach Nick Nurse said the return of Lowry makes it easier to substitute VanVleet and Siakam in and out of games.
The Heat entered its three-game trip looking to pick up quality road wins.
Jimmy Butler delivered a triple-double to beat Toronto, then turned his focus to Miami's next opponent with an unbeaten home record. That should be another great game, while we will see if the Heat can get their first win on the second night of a back to back set all season.
Bam Adebayo scored 18 points, Winslow had 17 and Kelly Olynyk 16 as the Heat snapped the Raptors' season-high winning streak at seven games, and became the first visitors to win north of the border this season.
Lowry had offseason surgery to fix ligaments in his left thumb.
"We have to figure out how we play, myself and Serge figuring out where to be at", Lowry said after the game Tuesday.
"That's rhythm. I missed shots, I didn't force anything, everything I shot came within the offence and honestly a lot of those threes went in and out, lay-ups".
"That's awful. That's rhythm", said Lowry, whose animated arguing at the officials was in mid-season form. Lowry had 12 points and 11 assists in 41 minutes.
Although the first game was one that saw the Heat get a win in Brooklyn on Sunday, which did give the Heat a day off for rest, the imminent second half of a Tuesday/Wednesday back to back will take place on Wednesday in Boston.
Toronto trailed 107-100 after Winslow's layup with 1:59 to go in the fourth.
Two shots finally fell for Lowry from the field in the fourth quarter, and he also bullied his way to the free-throw line repeatedly, resulting in a 10-point quarter as the Raps challenged for the lead. But where the Heat really shone was on the defensive end. Butler pulled up for a 3 over Powell, but his shot bounced off the rim, sending it to overtime.
Heat: Miami was without guard Goran Dragic (strained right groin).
Guard Dion Waiters was active and in uniform Tuesday, but he did not play. Waiters was suspended for 11 of the Heat's first 18 games, costing him about $920,000, pending appeals.
Butler went to work in OT, scoring eight unanswered points in the first 55 seconds.
Gasol drilled a three-pointer, slapping his thigh in celebration, that capped a 16-8 Raptors run and pulled Toronto to within a point midway through the second quarter. His only points came on a pair of free throws with 3:40 left in the second.
The defending National Basketball Association champions went 9-2 without Lowry and have won a season-high seven straight overall. The Heat are 13-0 when they outrebound their opponent.