Stephenson also grabbed 10 rebounds while Paul George added 23 points as Indiana defeated the Knicks 4-games-to-2 and gained the conference finals for the first time since 2004.
Roy Hibbert contributed 21 points, 12 boards and five blocks for Indiana.
The Pacers now go on to face the top-seeded Miami Heat in the East finals.
Carmelo Anthony drained 39 points, but only four came in the final quarter for New York. The Knicks superstar turned the ball over three times down the stretch, contributing to Indiana's triumph.
Iman Shumpert netted 19 points and J.R. Smith added 15 in the loss.