After a pair of sleepy five-game playoff series, the Celtics kicked off the Eastern Conference finals with an electric overtime thriller Tuesday night at TD Garden.

Boston was pushed to the brink by the lightning-paced, high-scoring Indiana Pacers, but Joe Mazzulla’s squad survived, winning 133-128 to take a 1-0 lead in the best-of-seven series.

Jaylen Brown drilled a game-tying 3-pointer with 5.7 seconds remaining to force overtime, and Jayson Tatum scored nine of his game-high 36 points in the extra session to help the Celtics pull away.

All five Celtics starters finished with at least 15 points, with Jrue Holiday notching 28 on 10-of-16 shooting (4-for-8 from three) and Brown scoring 26. Holiday also added eight assists, seven rebounds and three steals in his best all-around performance of the postseason.

Holiday, Tatum and Brown all played at least 44 minutes for Boston, which improved to 9-2 in the playoffs. Game 2 is Thursday night on Causeway Street.

The Celtics withstood a similarly balanced scoring output from the Pacers, who led the league in points per game during the regular season. Seven different Indiana players scored in double figures, with Tyrese Haliburton leading the way with 25 points and 10 assists.

Pacers head coach Rick Carlisle called the Celtics “impossible” to defend during his pregame news conference, and they looked that way in the opening minutes.

A rim-rattling Brown dunk seconds into the game — off a Tatum steal — ignited an early 12-0 run for Boston that also included 3-pointers from Holiday and Al Horford.

The Pacers, two days removed from the best playoff shooting performance in NBA history in Game 7 against the Knicks, missed their first six shots before finding their stroke. Indiana quickly trimmed Boston’s lead and trailed 34-31 at the start of the second quarter, buoyed by 11 first-quarter points off the bench Obi Toppin.

Indiana found success targeting Boston’s backups during that flurry, scoring against Payton Pritchard and Sam Hauser on three successive possessions. But Pritchard with responded one 3-pointer late in the first and another early in the second, then pulled out a nifty juke to hit a midrange jumper over T.J. McConnell.

The Celtics built their lead back to double digits four minutes into the second quarter, but difficulties defending big man Myles Turner caused that to swiftly evaporate. Turner scored 12 straight points for the Pacers, all with Horford off the floor, exploiting a one-sided matchup against backup Celtics center Luke Kornet.

Kornet typically is Boston’s third option when starting big Kristaps Porzingis is healthy. Porzingis reportedly could return as Game 4 of this series, but he’s missed the last seven games with a calf strain.

Kornet was better in his second-half minutes, though, and was a plus-2 for the game, compared to minus-8 and minus-15 for fellow backups Hauser and Pritchard, respectively.

A dunk by ex-Celtic Aaron Nesmith pulled Indiana even with 2:43 remaining in the half, and the teams proceeded to trade clutch threes in the final second, with Haliburton countering White’s second-chance trey with a towering 35-footer. The two high-octane squads entered halftime tied at 64-64.

Both shot better than 50% from the floor over the first two frames, but the Pacers owned a clear edge from beyond the arc (53.3% to Boston’s 31.8%) after their shaky start.

Brown, Tatum and White all were in double figures for Boston at half.

Five quick points from Haliburton out of the break gave Indiana its first lead of the night, but the Celtics responded with a 7-0 run to vault back ahead. After a Horford three, Brown slithered past Turner for a layup, then forced a turnover at the other end to spring Tatum in transition.

White, Brown and Holiday then powered a 16-2 run that gave Boston its largest lead yet, 90-77. The Celtics succeeded in attacking the basket during that spurt, drawing five fouls in a span of eight possessions, and Brown delivered a defensive highlight when he swatted a Nesmith 3-pointer into the Boston bench.

Nesmith, Boston’s first-round pick in 2020, finished with 14 points and four turnovers and fouled out in overtime.

The Celtics missed five of their 13 free throws in the third quarter, however, keeping Indiana within striking distance. And again, the Pacers rallied. Down 92-79 late in the third, they ripped off eight straight points, then cut the deficit to one with an off-balance, buzzer-beating three by Haliburton.

Seconds into the fourth, it was 95-94 Pacers. The Celtics pulled back ahead on a Tatum jumper and led by five after 10 straight points from Tatum and Holiday, but Indiana drew even again on a Turner three with 5:43 remaining.

Indiana led by three with a minute remaining. Two Brown free throws cut that to one, but Aaron Nembhard hit a stepback over Horford on the next possession. After Tatum missed a straightaway three that would have tied the game with 14.1 left, forced a Nembhard miscue on the ensuing inbounds pass to give Boston another shot.

Out of a Mazzulla timeout, Holiday found Brown in the corner for a three that sent the Garden crowd — rabid all night — into hysterics.

Haliburton nearly delivered another highlight-reel 3-pointer as time expired, but it missed the mark, sending the game to overtime tied at 117-117.

Down 123-121 with 1:12 remaining in the extra session, Tatum drove baseline for a tough layup, drawing a foul on McConnell and sinking his and-1 free throw. Holiday promptly forced a turnover, and Tatum buried a three put Boston up four.

Haliburton, Indiana’s All-Star point guard, buried his face in his palms as he walked back to the Pacers bench. Indiana now will look to replicate what Miami and Cleveland did in the previous two rounds and beat Boston on its home floor in Game 2.