Saturday night, however, the Raptors turned the tables and beat the Celtics 113-97 at TD Garden in a game Toronto led wire-to-wire. So, what changed?
"We've got pros," Raptors guard Kyle Lowry told ESPN. "We've got guys who don't care what people say. We've got guys that kind of just don't give a f--- and just go out there and work.
"We have guys that just don't care. We are going to go play. No matter what, where, how, we're going to go play."
The Raptors have had no choice but to adopt that mentality, as they have been dealing with one injury after another all season long. Toronto is currently without emerging star Pascal Siakam, starting center Marc Gasol and key reserve Norman Powell -- three of the team's top seven players -- because of injuries that have them all out indefinitely.
The top eight players in Toronto's rotation -- those three, plus Lowry, VanVleet, Patrick McCaw, Serge Ibaka and OG Anunoby -- have all missed at least one game, and all but Anunoby have missed at least five.
In total, the Raptors entered Saturday having lost 103 games to injury this season -- tied for fourth most in the NBA. The three teams above them -- the Golden State Warriors, Washington Wizards and Portland Trail Blazers -- all have losing records. The Raptors, on the other hand, sit in fourth place in the Eastern Conference, one game behind the Celtics in third and two behind the Miami Heat in second.
"We have a lot of talent," VanVleet said. "We have a lot of unselfish guys with a lot of talent that play hard and play together, and we have great coaching to put us in good positions. ... If you go out there and play as hard as you can, you have a chance on any given night."
For the most part, Toronto has done that. It has allowed the Raptors to survive the injuries, and it also has led them in several memorable comebacks -- most notably last Sunday's recovery from a 30-point deficit late in the third quarter to win at home against the Dallas Mavericks. On this night, though, it actually was the opposite, as the Celtics repeatedly cut their game-long deficit to three or four points -- only for the Raptors to respond with a run to push their lead back out to double-digits again every time.
They were able to do so thanks to contributions across the board, and from some unlikely sources -- including McCaw, who had his best game as a pro, finishing with 18 points, seven rebounds and eight assists in 43 minutes, while rookie Brissett had four points and six rebounds in 15 minutes.
"They just came out the gate, and we weren't ready," said Celtics guard Marcus Smart, who had seven points in 23 minutes off the bench in his return from an eight-game absence due to a double eye infection. "We were playing catch-up the whole game, and when you're playing catch-up like that against a really good team, it's tough.
"They made every right play out there, and you've got to give credit to Toronto. We came into their house on Christmas Day, a big game and won, and we knew coming into this game they weren't going to take that lightly. We just weren't prepared."
The Raptors were able to break the game open multiple times in the second half by repeatedly attacking Enes Kanter in the pick-and-roll. Kanter -- one of the league's premiere offensive rebounders but who struggles against good pick-and-roll operators -- kept dropping into the paint, and both Lowry (who finished with 30 points on 10-for-17 shooting, including 5-for-10 from 3-point range) and VanVleet (who had 18 points and went 4-for-9 from deep) took advantage. Celtics rookie Grant Williams had a rough night defensively as well.
"We were just going at the matchups and kind of going with what was working," Lowry said with a smile.
"They were great in the pick-and-roll all night," Celtics coach Brad Stevens said. "They destroyed us. ... We have to be much better defending that."
That won't be of concern to the Raptors, though, who simply are trying to survive until they can get Siakam, Powell and Gasol back and judge what, exactly, their team looks like before the NBA's trade deadline in early February.
In the meantime, the Raptors will keep trying to grind out victories -- and will wait to see where they sit in the bigger picture in the competitive Eastern Conference until they can get healthy.
"We don't know," Lowry told ESPN when asked how good the Raptors can be. "We'll figure it out, I think, as the year goes on. It's too early to even kind of ... I think we learned last year to stay in that even-keeled and whatever happens, happens, and we'll figure it out.
"I think April, May and June -- that's when we really want to be our best team."