Jalen Brunson has sparked one of the NBA's greatest post-season comebacks, a rally from a 22-point deficit in the fourth quarter, and finished with 38 points as New York beat Cleveland 115-104 in overtime in Game 1 of the Eastern Conference finals.

After a record-setting run through the first two rounds, the Knicks were going nowhere for 40 minutes against the Cavs on Tuesday (Wednesday AEST), trailing 93-71 with 7:52 to play. But Brunson relentlessly attacked James Harden to spark an 18-1 run and he tied it at 101 on a basket with 19 seconds remaining in regulation.

The home side then opened OT with a 9-0 run as a delirious crowd at Madison Square Garden danced and screamed in the aisles. New York moved within three wins of their first NBA Finals appearance since 1999.

Mikal Bridges added 18 points and three Knicks scored 13, including OG Anunoby, who came on late after struggling most of the way in his return after missing two games with a strained right hamstring.

Donovan Mitchell scored 29 points for the Cavaliers, who seemed well on their way to a third-straight road win before their late collapse.

New York won their eighth game in a row and will host Game 2 on Thursday.

The Knicks had outscored Atlanta and Philadelphia by a combined 194 points, the largest margin ever through a team's first 10 post-season games. But after not playing since May 10, when they finished their second-round sweep of the 76ers, New York misfired most of the night, looking like the rust hurt more than the rest helped.

They were four for 23 on three-pointers through three quarters and then had a horrible start the fourth. But a year after coughing up a 14-point lead in the final minutes of regulation and losing to Indiana in overtime in Game 1 of the conference finals on their home court, the Knicks found their offence just in time.

The only bigger fourth-quarter playoff comeback in the last 30 years was when the Los Angeles Clippers rallied from 24 down to beat Memphis in Game 1 in 2012.

New York came from 20 points behind three times last year in the post-season. Those were their largest comebacks on record since 1969-70, when they won their first of two NBA titles.