By Matthew Geagan, CBS Boston

BOSTON (CBS) — The defending NBA champion Toronto Raptors have just two losses in the NBA’s Orlando bubble. Both of those defeats have come at the hands of the Boston Celtics.

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The Celtics reaffirmed their “title contender” status by taking Game 1 of the Eastern Conference semifinals on Sunday, handing Toronto a 112-94 beat down to take a 1-0 series lead. The Celtics ran out to an early lead and never looked back, leading by as many as 19 points in the first quarter and 22 in the third.

Some fine defense and three-point shooting gave Boston its fourth win in five games against the Raptors this season. Six players finished in double figures for Boston, with Jayson Tatum and Marcus Smart both leading the way with 21 points apiece. Kemba Walker was magnificent again, scoring 18 points off 6-for-11 shooting, including 4-for-7 from downtown, to go with 10 assists, while Jaylen Brown added 14 points despite battling foul trouble in the second half.

Smart went 5-for-9 from three-point range on Sunday after hitting just two threes total in the first round against the 76ers.

“Marcus today was unbelievable on both ends,” head coach Brad Stevens said after the win. “I thought all our guys played with great purpose, great enthusiasm. We just have to clean some stuff up.”

The Celtics built that 19 point lead despite Tatum scoring just two points in the opening frame. Smart dropped 10 points in the first quarter while Brown had nine as Tatum (hitting just one of his first four shots) struggled. Boston led 39-23 after the first quarter.

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The Boston defense came out strong and flummoxed Raptors shooters throughout Sunday’s game, with Toronto shooting just 29 percent in the first half and 37 percent overall. The Raptors were just 10-for-40 from three-point range, while the Celtics hit 17 of their 39 shots from downtown (44 percent). Toronto’s transition offense was thrown out of whack by the C’s switch defense, which held the Raptors to just seven fast-break points on Sunday.

Paskal Siakam was a non-factor for Toronto with just 10 points off 5-for-16 shooting, while Fred VanVleet had just 11 points off 3-for-16 shooting. Kyle Lowry led the charge for the Raptors with 17 points, eight assists and six rebounds.

Boston led 59-42 at halftime thanks a Kemba 3 at the buzzer.

The Raptors pulled within 13 in the final moments of the third quarter, but Tatum hit a baseline jumper at the buzzer to put Boston back up by 15. Tatum scored nine points in the third, hitting four of his six shot attempts in the frame.

Boston got big games out of their big men, with Daniel Theis recording his first-ever playoff double-double with 13 points and 15 rebounds. Robert Williams III had 19 monster minutes off the bench, finishing with 10 points, five rebounds and two blocks..

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Game 2 is set for Tuesday.