Kyle Odister scored 15 points, including the decisive free throws in the closing seconds, as Cal Poly upended 11th- ranked UCLA, 70-68, at New Pauley Pavilion.
Dylan Royer paced the Mustangs (2-2) with 18 points, while Brian Bennett added 16 and Chris Eversley contributed a double-double with 15 points and 10 rebounds in Cal Poly's second win in three games.
"We have so much respect for this school, this program and this team," Royer said. "To be down (by 18 points) is a little discouraging, but we kept our heads up and we kept fighting."
Shabazz Muhammad finished with 15 points and 10 boards for UCLA (4-2), which has dropped two of three.
Travis Wear netted 14 points and Jordan Adams dropped in 13 in defeat.
The Bruins held a 29-27 lead at the break and opened the second half with a 22-6 run that included nine points by Wear and seven by Muhammad to take a seemingly comfortable, 51-33, lead with about 12 minutes remaining in the game.
But Cal Poly did not quit, battling back with a 30-12 push to knot the game at 63-63 on back-to-back 3-pointers by Royer around Wear's layup.
Royer had another three-point attempt rim out after the teams traded baskets, but Eversley was there to tip-in the rebound to give the Mustangs a 67-65 edge with just under two minutes remaining.
Cal Poly later held a 68-66 lead after Larry Drew III went 1-for-2 at the foul line with 25 seconds left, but Eversley turned the ball over and Adams tied the game at 68 with a layup.
Norman Powell, though, fouled Odister on Cal Poly's ensuing possession and he sank both of his free throws with 11 seconds remaining.
Powell failed to atone for his gaffe with a missed 3-pointer on the other end, and after the rebound went out of bounds off a member of the Mustangs with five seconds showing to keep the ball in the hands of UCLA, Adams also had a three-point attempt rim out at the buzzer to seal the win for Cal Poly.
"Tonight, we played pretty hard," Muhammad said. "But at the end we just gave up. We were up 18 and there was a stretch where we gave up a lot of threes and fouled trying to get back on defense."
It was a one-possession game over the first four-plus minutes of action until the Bruins reeled off nine straight points to go on top, 16-9.
But UCLA would be held without a basket for nearly eight minutes while the Mustangs used the drought to regain a 20-16 edge on Odister's 3-pointer.
Adams was able to put an end to the dry spell with a triple on the Bruins' ensuing possession, and UCLA outscored Cal Poly, 13-7, for the remainder of the first half to take a 29-27 lead into the break on Drew's layup in the closing seconds.
It was Cal Poly's first-ever win against UCLA, which leads the all-time series, 5-1 ... The Mustangs shot 44.4 percent from the field and went 9- for-25 from three-points range ... UCLA shot 45.3 percent in the game and 5- for-13 from beyond the arc ...Wear and Powell each netted nine points in defeat.