The Celtics withstood a spirited effort by an injury-ravaged Cavaliers squad Wednesday night to book their third straight trip to the Eastern Conference finals.

Boston won 113-98 at TD Garden to eliminate Cleveland in five games.

Jayson Tatum finished with 25 points on 9-of-16 shooting, 10 rebounds, nine assists and four steals to lead the top-seeded Celtics, who also got a vintage performance from Al Horford.

The 37-year-old big man, making his sixth consecutive start in place of the injured Kristaps Porzingis, racked up 22 points, six 3-pointers, 15 rebounds (seven offensive), five assists and three blocks in by far his best game of the postseason.

Derrick White added 18 points, six assists and four rebounds for Boston, which improved to 8-2 in these NBA playoffs.

Cleveland, which was playing without starters Donovan Mitchell and Jarrett Allen and sixth man Caris LeVert, was competitive until late thanks to a stunningly effective outing by ex-Celtic Marcus Morris Sr.

Morris scored a season-high 25 points on 10-of-13 shooting and was 5-for-6 from 3-point range. Evan Mobley also gave Boston problems with 31 points, seven boards and two blocks, but Cavs points guard Darius Garland struggled, going 4-for-17 from the field and 0-for-4 from three.

The Celtics now can enjoy at least three days of rest before opening the East finals against either the New York Knicks or Indiana Pacers.

If Knicks-Pacers and the Western Conference semifinal between Denver and Minnesota both wrap up in six games, the Celtics’ next game would be Sunday. If either of those series goes seven, Boston would be off until Tuesday night.

The soonest the Celtics could know their next opponent is Friday night, when the Knicks will look to close out the Pacers on the road in Game 6.

A Celtics-Knicks matchup would mark the first time teams from Boston and New York have met in a conference final (or equivalent) since Red Sox-Yankees in the 2004 ALCS.

Time will tell whether the three- or five-day layoff will be long enough for Porzingis, who sat out the Cavs series with a soleus strain in his right calf. The 7-foot-2 difference-maker recently resumed basketball activities, and initial reports indicated the Celtics were hopeful to have him back in time for the East finals.

White scored 10 of the Celtics’ first 21 points Wednesday as part of all-around impactful first quarter that also included a blocked shot, a drawn charge and a slick assist on a Luke Kornet dunk.

Horford also turned in a strong early shift for Boston. He blocked one shot, forced two misses with strong contest, dished out an assist and drilled a 3-pointer before heading to the bench midway through the opening quarter.

The Celtics were sloppy with the ball late in the first, however, and struggled to defend old friend Morris, who scored as many points in the first nine minutes (seven) as he had in the first four games of the series combined.

Midway through the second, Morris was up to 14 points on 6-of-7 shooting, and the shorthanded Cavs led 48-43.

White and Horford took command during an ensuing timeout, passionately instructing their teammates while head coach Joe Mazzulla game-planned with his assistants. Then, they did the same on the court. The duo combined to score the next eight points to push Boston back ahead.

That surge also featured a flurry of hustle plays from both players — especially Horford, who blocked two Garland shots, grabbed two offensive rebounds and whipped the Garden crowd into a frenzy by leaping to save a loose ball out of bounds.

That roar grew louder when Tatum drilled a 3-pointer as time wound in the half, but his reaction drew a technical foul from referee Tony Brothers. The Cavs made their free throw, and Boston entered halftime up 58-52.

The Celtics stretched their lead to double digits midway through the third quarter, but the Cavs rallied to pull back within six, prompting a Mazzulla timeout. Tatum scored 10 third-quarter points, Payton Pritchard hit a pair of threes off the bench, and the Celtics led 85-78 entering the fourth.

Morris’ fourth 3-pointer of the night cut that deficit to three points moments later, but Cleveland couldn’t close the gap. Threes by Horford and White in quick succession and back-to-back buckets by Jrue Holiday helped Boston pull away and ice the series.