Trevis Wyche added 10 points and eight rebounds for the Peacocks (4-6).
It was the first meeting in 11 seasons between the schools that are separated by eight miles. Saint Peter's leads the series 32-26 after winning its fourth straight against the Terriers.
Antwon Portley's free throw with 3:20 left in the first half broke a 20-20 tie and started the Peacocks on a 9-0 run. Portley followed with a 3 and Welton scored the last four points after an Elias Desport jumper for a 29-20 lead.
The Terriers battled back to tie the game at 38 with 8:09 to play but Welton and Wyche combined for 10 points that made it 48-38 at 4:19 left.