MORAGA, Calif. (AP) -- Diamon Simpson took over a tough defensive matchup against Gonzaga and still had more than enough left for a career scoring performance.
Simpson had a career-high 29 points and keyed a 19-2 second-half run, and Saint Mary's handed Gonzaga its first conference loss in nearly two years with an 80-75 victory Monday night.
Simpson scored nine of the Gaels' final 15 points as they snapped the Zags' 26-game West Coast Conference winning streak and a 30-game winning streak against conference opponents including tournament play.
"We were just aggressive on defense the whole time," Simpson said. "We were definitely ready for them."
Ian O'Leary dunked with 1 second left and Saint Mary's fans stormed the court before the announcer told them to go back to their seats. Gonzaga's players had left for the locker room and then quickly returned to the floor, where Derek Raivio made two free throws following the administrative technical against the Gaels. The real celebration started after the buzzer sounded.
What a night for Gaels guard Wayne Hunter on his 21st birthday.
"All I can say is we won on Wayne's birthday," Simpson said.
Freshman center Omar Samhan scored a career-high 20 points, 12 in the second half, grabbed five rebounds and hit eight of nine free throws for Saint Mary's (10-9, 2-1), which ended a four-game skid against its conference nemesis.
"In the second half, we did not do a very good job of getting team shots early and then our defense just totally broke down, especially our post defense," Gonzaga coach Mark Few said. "It was nonexistent and those two guys just worked us over."
The Gaels had dropped 21 of 22 to the Bulldogs, who lost 89-81 on Saint Mary's home floor on Jan. 8, 2005, to end a 17-game winning streak in the rivalry -- Gonzaga's longest run against any WCC opponent.
Simpson's three-point play with 5:19 left made it 68-63, then Samhan scored on the Gaels' next possession. Simpson hit a 3-pointer with 2:35 left, then Saint Mary's missed five free throws in the final minute.
Gonzaga lost a conference game for the first time since a 73-70 defeat at San Francisco on Jan. 20, 2005.
"It's good," Saint Mary's coach Randy Bennett said. "Only two teams have beaten them in the last two years. We've played them close for a while. They are a tough team and hard to beat."
Josh Heytvelt returned to the starting lineup for Gonzaga (12-6, 3-1) and scored 12 of his 20 points in the final 5:06 of the first half. Heytvelt, who had eight rebounds, was guarded by Simpson in the second half and was held to four. Jeremy Pargo added 22 points and seven rebounds, making all eight of his free throws.
San Francisco, which won 72-71 at Pepperdine earlier in the night, took over sole possession of first place in the conference and is the WCC's lone unbeaten team.
Saint Mary's blew a late five-point lead in the last meeting, a 62-61 victory by Gonzaga in Spokane, Wash., on Feb. 6, 2006. The Zags won 68-60 on the Gaels' home floor while ranked No. 8 last season.
Simpson had six straight points -- with a three-point play and 3-pointer -- to tie it at 45 with 17:46 to play and start a 14-0 run. Hunter then hit a 3 to give the Gaels their first lead since late in the first half and he also converted three free throws at 15:17 to make it 53-45. Simpson also grabbed 11 rebounds and blocked two shots.
"He's not a 3-point shooter, but he was tonight," Few said, "and that's the way it is sometimes when the Zags hit the road."
The 6-foot-11 Samhan had six points during the big run, taking the ball hard to the basket and drawing fouls on Sean Mallon in the paint. Mallon sat down with his fourth foul at 11:56 and Samhan had a three-point play that made it 61-49.
The raucous Saint Mary's students hollered "Beat the Zags!" and held signs reading "Feed Raivio," filling the seats more than an hour before tipoff for the nationally televised game at sold-out McKeon Pavilion. An overflow crowd packed the 3,500-seat arena.
Few became the third-fastest coach to reach 200 victories with his team's 77-69 win at Santa Clara on Saturday night, but the Bulldogs missed a chance for only their second road win of the season.
Raivio struggled, going 4-of-14 -- 1-for-5 from long range -- for 12 points and dishing for only four assists. He scored his first basket of the second half with 12:20 remaining.
"We dug ourselves a hole, but we brought it back to one and I felt we had the game," Raivio said. "It seemed like they were trying to give it to us. We just didn't finish it off."