The Knicks vanquished their greatest foe. Now, they have to do it three more times.

Trailing by as much as 20 — and nine entering the fourth quarter — the Knicks staged a furious rally to send Game 1 of the Eastern Conference semifinals into overtime en route to a thrilling 108-105 win in Boston.

Mikal Bridges came alive in the overtime period with a blocked shot, a steal that led to an-and-1 dunk by Anunoby and a hit a clutch 3-pointer extend their lead to six points.

He saved his best for the final seconds, however, stealing the ball from Jaylen Brown to clinch the win.

Anunoby and Brunson led the way with 29 points apiece, while Bridges finished the night with eight.

Josh Hart and KArl-Anthony Towns added 14 points each, with Hart adding 11 rebounds and Towns 13.

The Celtics’ Brown and Jayson Tatum scored 23 each to lead Boston’s charge.