Toronto Raptors coach Nick Nurse did not feel "especially satisfied" despite the defending NBA champions beating the Boston Celtic 100-93 to level their series at 2-2.

Pascal Siakam and Kyle Lowry starred for the Raptors in the Eastern Conference semi-final playoff, leading them to a crucial Game 4 win on Saturday.

Siakam posted 23 points and 11 rebounds, while Lowry claimed a double-double of his own with 22 points and 11 rebounds.

The Raptors had suffered back-to-back losses at Walt Disney World Resort in Orlando, Florida, in the first two matches of the series, but following their buzzer-beating win in Game 3, they are back on level terms.

But Nurse was not getting carried away and he wants more from the Raptors as they look to take charge of the series.

"We don't think we're defending a title," said Nurse. "We're just trying to get this team to do what they can do at as high a level as they can.

"And that, to me, is the job. I don't feel especially satisfied about winning this game tonight or how we played.

"I think that's what we're supposed to do and this is what we're working for – to get these guys to play as hard as they can and play together to get the result, and just go back to work and try to do it a little better again tomorrow."

While the Raptors were grateful to tie the series, there was more than a hint of rueful thinking from the Celtics, particularly Kemba Walker.

The four-time NBA All-Star finished with 15 points and eight assists, but he shot just nine times and successfully converted one of six from three-point range as the Celtics routinely faltered from beyond the arc.

"I got to be more aggressive, I wasn't aggressive enough," he reflected. "That's unacceptable on my behalf, to be honest. There's no way I can just be taking nine shots. That's unacceptable.

"Honestly, man, I thought we had great looks. I thought we had great looks throughout the whole game.

"We just really missed. We missed a lot of open ones that we know we can make. Like I said, we've got to make them. We have to make shots. When guys get shots, when guys are open, we've got to knock those shots down.

"We'll do better. We'll do better."