With Joel Embiid sidelined and the Boston Celtics feasting early, the Philadelphia 76ers looked in trouble early on Monday.

But an MVP revival from James Harden and a late Celtics gaffe saw the 76ers escape with a 119-115 Game 1 win in the Eastern Conference semifinals as their MVP finalist watched in street clothes. Harden scored a playoff career-high 45, including the go-ahead 3-pointer with 8.4 seconds remaining, as Philadelphia overcame a porous effort on defense with Embiid on the bench with a knee injury.

Harden's 3-pointer marked the crescendo of a frenetic final minute that saw the Celtics cede control of the game with an unforced error. Boston held a 113-112 lead and possession with less than 40 seconds remaining. But Celtics guard Malcolm Brogdon threw the ball toward the backcourt to Philadelphia's Tyrese Maxey, who ran unimpeded to the other side of the floor for a go-ahead dunk.

Jayson Tatum responded with a pair of free throws on the next Celtics possession to retake the lead for Boston at 115-114. But Harden's 3 on the next Philadelphia possession gave the 76ers the lead for good. It was a stunning end to a game where Boston held a significant advantage at home playing against a team missing its dominant center.

Celtics torch 76ers defense early

The game got off to a great start for Boston, which took full advantage of Embiid's absence in the first quarter. The Celtics feasted on a defense playing without its rim protector and three-time All-Defensive team member. They hit 15 of their first 16 field goals en route to a 17-of-20 first-quarter effort. Five of those makes arrived on open dunks as Boston scored a season-high 26 first-quarter points to take a 38-31 lead.

But Harden loomed even as Boston took the early advantage. The 2017-18 MVP has taken a secondary role on offense since joining Embiid in Philadelphia. As Embiid won his second straight scoring title, Harden led the league with 10.7 assists per game this season. But he's more than comfortable as the go-to guy and looked very much like his vintage self early and throughout against Boston.

James Harden hot early, throughout

Harden got off to a 5-of-5 start from the field while scoring 12 of Philadelphia's first 16 points. By halftime, he'd tallied 21 points on a 9-of-14 shooting effort while helping cut the 76ers' deficit to 66-63. Philadelphia then tied the game at 87-87 to end the third, setting up the frenetic fourth quarter that saw him seal the win at TD Garden.

Harden finished with 45 points, 6 assists, 1 rebound and 2 steals. He shot 17 of 30 from the floor, including 7 of 14 from beyond the 3-point arc. Maxey finished with 26 points, while De'Anthony Melton added 17 points off the bench. Tobias Harris scored 18 points while shooting 8 of 16 from the field, as Paul Reed posted 10 points and 13 rebounds while starting for Embiid.

But he was no substitute for Embiid, most notably on the defensive side of the court. Boston's offensive stats look like those of a winner. The Celtics cooled off from their hot start, but still shot 58.7% from the field while hitting 17-of-18 free-throw attempts (94.4%).

Tatum challenged Harden for top billing while tallying 39 points, 11 rebounds and 5 assists. Philadelphia struggled to defend him on the interior or from outside as he shot 14 of 25 from the field and 4 of 5 from distance. He was also able to return for the game's final stretch after a low blow from P.J. Tucker left him writhing in pain in the fourth quarter. The play didn't lead to a flagrant foul as officials appeared to deem the blow inadvertent. It did result in tensions rising between familiar rivals.

But Boston ultimately couldn't overcome the league's best 3-point shooting team as the 76ers shot 17 of 38 from beyond the arc (44.7%). They were also perfect (12 of 12) at the free-throw stripe. And now they have a 1-0 series lead.

Embiid's now missed two straight playoff games with the knee sprain after previously sitting Game 4 against the Brooklyn Nets in the Sixers' first-round sweep. His status for Game 2 isn't clear. But the 76ers have a lot more breathing room now having stolen Game 1 without him and Games 3 and 4 eventually shifting to Philadelphia.

The pressure will squarely on the Celtics for Wednesday's Game 2.