With the win, Saint Mary's improves to 15-6, 7-2 West Coast Conference, while Portland drops to 9-14, 4-6 WCC.
"We rebounded the ball well and assisted on over half of our baskets," said head coach Paul Thomas. "We made plays when we needed to and did what we had to do, to get the win. I'm proud that we accomplished that goal tonight."
Saint Mary's got double-doubles from Jackie Nared (16 points, 10 rebounds) and Morgan Hatten (13 points, 11 rebounds). Kate Gaze added nine points and four assists.
Portland was led by Annika Holopainen with 26 points while no other Pilots reached double figures.
The Gaels used an early 8-0 run to take an early lead as coach Thomas went four players deep into the bench in the first six minutes of the game. SMC built a 22-12 lead after a Hayley Hendricksen basket in the paint. The Gaels ended the half on a 9-1 run to take the 32-18 halftime lead.
Saint Mary's led by as many as 15 points in the second half, but the scrappy Pilots never gave in and chipped away at the SMC lead. The Pilots got the deficit down to 10 points with 13 minutes left and pulled within 43-39 with 8:06 on the clock.
Portland capped off its rally by taking the lead 43-42 with 7:22 left and later led 48-45 with 3:15 remaining. SMC kept its composure and Gaze knocked down two free-throws to pull SMC within one.
On the next possession, Andrea Bailey drew a charge and then scored on the other end to give SMC a 49-48 lead. Bailey played key minutes as the Gaels were without the WCC's leading rebounder in Danielle Mauldin.
With the Gaels up by one and under a minute left, Nared drove the lane and put up an acrobatic shot, drawing the foul and falling to the floor for an and-one. Nared made the free-throw and SMC went up 54-50 with 55 seconds left.
POR connected on a three to cut it down to one, but Hatten drove the lane and scored perhaps the biggest basket of the game and giving SMC the 56-53 lead. The Gaels were able to step on defense and get the final two stops of the game and a Nared rebound and free-throws iced the game.
Bailey played a season-high 22 minutes and scored four points with five rebounds. Carli Rosenthal added five points and seven rebounds while Hendricksen added five points and two rebounds.
Saint Mary's outrebounded Portland 45-27 and the Gaels had 12 assists on their 20 field goals.
Saint Mary's is back in action on Saturday afternoon when it hosts BYU at 2:00 p.m. in McKeon Pavilion.