The Colonials (27-3) advance to face Harrisburg, a 49-48 winner over Whitehall. Chambersburg finishes the year at 22-8.
After Mark La Pera missed a pair of free throws with 19.2 seconds to play, Chambersburg found itself with the ball, trailing by one.
Larry Johnson missed a jumper from the corner and Alex Hart missed the putback attempt. But teammate Chris Clever was there, and after grabbing the rebound, was fouled. Clever hit both foul shots for a 59-58 lead with 3.9 seconds left.
After a timeout, the Colonials set up for the final shot.
A full-court pass from beneath the basket by Kevin Gall was out of the reach of Salmons. But sophomore Bill Guess saved the ball from going out of bounds and sent it back to Salmons, who checked the clock and stuck the game winner.
"He's a clutch player who has made clutch shots for us in the past," said P-W coach Al Angelos. "He's a big-time player now. This is a breakout game for him."
"I think the save by (Guess) really won the game for us," Salmons said. "If it weren't for Bill, we would have never gotten the shot."
Chambersburg fell behind by as many as 12 points in the fourth quarter, but battled back.
Cody Carbaugh and Austin Keggereis hit back-to-back 3-pointers to ignite a Trojans' rally, which reduced the deficit to one heading into the final minute.
Chambersburg coach Mark Cubit declined comment.
Keggereis led the Trojans with 15 points. Clever and Hart scored 12 each.