By Matthew Geagan, CBS Boston

BOSTON (CBS) — The Celtics have made it look easy against the Toronto Raptors this season, with Sunday’s Game 1 victory Boston’s fourth win in five tries against the defending champs. Sunday’s 112-94 win was another convincing victory from start to finish for Boston, and so far in their two bubble games against Toronto, the Celtics have not trailed against the Raptors.

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But the Celtics know better than to take Sunday’s Game 1 results and feel great about being up 1-0. The Celtics may be 5-0 this postseason, but they know just how quickly things can change.

Jayson Tatum, who dropped 21 points on the Raptors on Sunday, was reminded during his postgame interview that the C’s were 5-0 last postseason and then dropped four straight to fall to the Milwaukee Bucks in the second round. It wasn’t a pleasant reminder for Tatum, but he understands that last season’s downfall was a great teaching point for the team.

He also says this year’s squad is much, much different than last year’s disappointing Celtics.

“We just won a game – did you have to bring last year up?” Tatum said with a chuckle. “This is just different; a different environment and a different team. We won our first five games last year and lost four in a row. Last year is behind us. This is different all around.

“We know it’s not going to be easy,” he said. “They’re the defending champs for a reason. We just need to take it one game at a time.”

The biggest difference, of course, is switching out Kyrie Irving for Kemba Walker. Irving is a much more skilled player, but Walker’s demeanor is a much better fit for a team littered with young talent. Walker is A-OK taking a backseat and watching Tatum and Jaylen Brown become stars in the league.

It helps that Walker is pretty good as well, contributing 18 points and 10 assists in Sundays blowout victory.

The Celtics now have two convincing wins against the Raptors over the last three weeks, Toronto’s only two defeats in that span. Toronto was riding an eight-game win streak until they ran into the Celtics on Sunday.

While the C’s made it look easy in Game 1, they aren’t going to rest on the results of just one game. And as head coach Brad Stevens pointed out in his postgame press conference, Boston was far from perfect on Sunday.

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“We didn’t play great offense. We turned it over a lot and I thought we missed some reads in both halves, but more in the first. We just made timely baskets,” said Stevens. “Tatum’s steal and Kemba’s three at end of half, Tatum hitting the shot at end of the third. We were able to keep separation that way. We need to go back and look at how we can play better.

“But guys had a good mindset and they kept guarding no matter what happened,” he added.

Though the Celtics held the Raptors to just seven fast-break points — an impressive feat against a team that averaged an NBA-best 18.8 points on the fast-break — Stevens questioned that figure. The Celtics were able to slow down Toronto’s furious offensive attack and frustrated their scorers throughout by switching constantly on defense, but Stevens wants to see an even better defensive performance in Tuesday’s Game 2.

“It was not as good as the last time we played them,” Stevens said of Boston’s transition D. “But it’s a huge key to us being a good basketball team.”

“It was OK, it could definitely be better,” said Smart, who was everywhere on defense while scoring 21 points on Sunday. “You can’t give those guys those transition plays where they get energy, momentum and get to the free throw line. It was OK, but there is a lot that could get better. We’ll watch the film and clean it up.”

The series is far from over, and Stevens was sure to hammer that point home on Sunday. The Celtics can’t take anything lightly against the Raptors, who will be eager to pounce early in Game 2.

But if the Celtics can continue to smother the Raptors on the defensive end and keep up its balanced offensive attack — with six players scoring in double figures on Sunday — then Boston should continue to prove that they are indeed title contenders.

“I believe in each and every one of those guys in the locker room,” said Tatum. “We’ve spent so much time together down here, putting in work every day. We came prepared. It’s not going to be perfect every game. We know how good Toronto is and how tough they are. This is one game and we can’t think about it no more – we have to think about the next one. We know they’re going to come out harder and we have to match their intensity.”

The Celtics are one confident bunch after Sunday’s victory, and they should be. Not a lot of teams can brag about beating the Raptors nearly every time they’ve played.

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But at the same time, Boston isn’t going to let any over-confidence creep in to the locker room. They learned that lesson last year, and are much better prepared to combat it this time around.