James Harden hit the go-ahead 3-pointer with 18 seconds left in overtime and scored 42 points to help the Philadelphia 76ers stave off a wild Boston Celtics comeback in a 116-115 victory on Sunday that evened their playoff series at 2-2.

Marcus Smart's potential winner was a tick too late and the Celtics now head home for Tuesday's Game 5.

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Joel Embiid goes up for a shot

Philadelphia 76ers' Joel Embiid goes up for a shot against the Boston Celtics during the second half of Game 4 in an NBA basketball Eastern Conference semifinals playoff series, Sunday, May 7, 2023, in Philadelphia. (AP Photo/Matt Slocum)

The Celtics rallied from 15 points down with 2 minutes left in the third quarter in hopes of seizing control of the series.

The Sixers were on the brink of defeat numerous times over the final 17 minutes, none more than when Joel Embid connected with Smart on a driving, one-handed bank shot with 1:49 left but was whistled for an offensive foul. The play was reviewed and the call stood. Boston kept its 112-111 lead with 1:49 left in OT.

Embiid kept his composure and eventually got to the line to sink the go-ahead free throws with 59 seconds left and the season in the balance.

Embiid had 34 points and 13 rebounds.

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James Harden vs Marcus Smart

Philadelphia 76ers' James Harden (1) reacts past Boston Celtics' Marcus Smart during the second half of Game 4 in an NBA basketball Eastern Conference semifinals playoff series, Sunday, May 7, 2023, in Philadelphia.  (AP Photo/Matt Slocum)

They went to overtime tied 107-all after Smart was short on a 3 at the horn that was one of the few clutch shots Boston missed in the quarter. The Celtics trailed by 15 points with 2 minutes left in the third before they sucked the life out of the Wells Fargo Center.

The fun began when Smart and Jaylen Brown buried consecutive 3-pointers and Jayson Tatum attacked the rim for a bucket that wiped out an eight-point hole in 90 seconds. Al Horford put them ahead 98-90 — on a possession that started on the other end when Tyrese Maxey had his shot blocked — and shimmied for the crowd as boos rained on him.

Yes, the 76ers had home court but fans tensed up as memories all those second-round exits since 2001 stirred inside the building. Smart and Malcolm Brogdon hit consecutive 3s for a 105-100 lead.

Derrick White walks off the court

Boston Celtics' Derrick White walks the court during overtime of Game 4 in an NBA basketball Eastern Conference semifinals playoff series against the Philadelphia 76ers , Sunday, May 7, 2023, in Philadelphia.  (AP Photo/Matt Slocum)

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But it was P.J. Tucker, the heart and guts of the Sixers, who again did the dirty work on a defensive rebound a bucket. He made the free throw with 1:05 left and the tie game gave them new life.