TEMPE, Ariz. — UNLV coach Mike Sanford said his players believed they could win.

Arizona State couldn't believe it lost.

UNLV's Malo Taumua blocked a field goal to give the Rebels to a 23-20 overtime upset of No. 15 Arizona State on Saturday night. Taumua's block on a 35-yard attempt by Thomas Weber came after Kyle Watson kicked a 20-yarder on the Rebels' overtime possession.

"We believed we were going to win," said Sanford, who wept on the field as the jubilant Rebels celebrated with a throng of red-clad fans in a corner of Sun Devil Stadium. "Our players believed. Our coaches believed. And that's how you win those games. It's not by accident."

The loss took the luster off the Sun Devils' long-awaited game against No. 2 Georgia next Saturday. Arizona State had hoped to use a victory over the Bulldogs to catapult themselves into the national title hunt.

Instead, the Sun Devils (2-1) probably won't even be ranked by the time the Bulldogs arrive.

"It was a nightmare," coach Dennis Erickson said. "It's sickening.

"It starts with me. I didn't have them ready to play. I'll take the blame."

For the Rebels, it will go down as one of the great victories in the school's sometimes checkered football history. It was only Sanford's eighth win — against 30 losses — in four seasons.

The game capped a shocking four-game sweep of the Pac-10 by the Mountain West Conference on Saturday. Elsewhere, Texas Christian beat Stanford 31-14, New Mexico knocked off Arizona 36-28 and Brigham Young hammered UCLA 59-0.

"I am overwhelmed," Sanford said. "But at the same time, I knew we were going to win the game."

UNLV (2-1) bolstered its belief on a spectacular play by freshman receiver Phillip Payne — a homegrown Las Vegas product — in the final minute of regulation.

With 18 seconds left, Payne made a leaping one-handed grab of an 8-yard touchdown pass from Omar Clayton. The catch capped a 10-play, 74-yard drive that lasted 2:45, with Clayton going 6-of-8 for 70 yards.

Clayton had taken a shot to the jaw in the first half, and Sanford said Clayton had been X-rayed at halftime to see if the jaw was broken.

"It turned out he did not have a broken jaw, as you could see the way he played," Sanford said. "I thought he grew up a lot tonight."

Clayton completed 19 of 31 passes for 191 yards and two touchdowns.

For the Sun Devils, this was supposed to be a tuneup for Georgia. But they couldn't put the Rebels away.

Arizona State looked safe when Rudy Carpenter hit Kyle Williams for a 49-yard touchdown pass to put ASU ahead 20-10 early in the third quarter.

"No disrespect to them, but we let them hang around in the game, and look what happened — they beat us," ASU safety Troy Nolan said.

The Rebels served notice that they weren't going to be pushovers late in the second quarter. Carpenter threw an interception to UNLV defensive back Beau Orth, who returned it 9 yards to Arizona State 7.

Like Payne, Orth is a freshman and a Las Vegas product.

Three plays later, Clayton threw a 2-yard touchdown pass to Payne, who outleaped cornerback Omar Bolden in the end zone with 33 seconds to play in the half.

"I am very proud of our football team," Sanford said. "They were a team that just kept fighting, kept going."

The Sun Devils responded with a quick four-play, 33-yard drive capped by Weber's 49-yard field goal as time expired in the first half, giving ASU a 13-10 halftime lead.

The Sun Devils had vowed that they would not look past the Rebels to next week's visit by the Bulldogs — but it certainly looked that way.

Arizona State moved the ball easily on its first drive but stalled near the Rebels' goal line, extending a troubling early season trend. ASU had first-and-goal at the UNLV 9, but gained only 6 yards and had to settle for a 20-yard field goal by Weber.

That was a bad sign against a team tied for last in the nation in red zone defense. It was the first time in six attempts this season that the Rebels had stopped a team inside its 20.

On its next drive, Arizona State didn't come close to the end zone, giving up back-to-back sacks to a team that had one sack through the first two games.

The Sun Devils certainly didn't look like they were capable of beating the No. 2 team in the country. As it turned out, they couldn't even beat the lightly regarded Rebels, who were a lot better than advertised.

"We're going to take all this aggression and anger and apply it to practice, and hopefully play a great game next week," said Carpenter, who finished 13-of-23 for 242 yards and two touchdowns, and he was intercepted once.