Viejas Arena was buzzing Sunday evening, with a sold-out crowd seeing a No. 1-seeded team in the NCAA Tournament in danger of losing.

Except it wasn’t happening on the floor in the building where they were sitting and watching Arizona; it was on the arena video board, which was showing cut-ins of Florida struggling to defeat Iowa some 2,100 miles away in Tampa, Fla.

When a replay of the final play in the Hawkeyes’ victory was shown during the first media timeout of the second half, the heavily pro-Arizona crowd cheered loudly.

At least part of their joy likely stemmed from the fact it wasn’t happening — again — to their beloved Wildcats.

Until it almost did.

Comfortably in front at the time Florida lost, the Wildcats scored the next seven points to take an 18-point lead with just under 15 minutes remaining.

Not 10 minutes later, it was a four-point game. But a big finish produced a 78-66 victory for Arizona, which improved to 34-2 and advances to play No. 4 Arkansas in a West Region semifinal Thursday in San Jose. The other semifinal matches No. 2 Purdue against “Cinderella” Texas, the No. 11 seed led by former Arizona coach Sean Miller.

The loss by Utah State (29-7) ended the Mountain West’s brief stay in the tournament and also the Aggies’ time in the conference. Utah State will be leaving this summer along with four other MW schools, including San Diego State, for a slimmed-down version of the Pac-12.

“You can’t simulate the size,” Utah State coach Jerrod Calhoun said. “That’s the difference in the game, is their physicality and size.”

Arizona didn’t play particularly well for most of the night, especially in the first half when it missed 22 of 31 shots, including 12 of 13 at one point. But Utah State was unable to take advantage, primarily because the Aggies were 1 of 12 on 3-point attempts in the opening half (after going 2 of 16 in their opening-round win here Friday).

Just when Arizona appeared on the verge of a blowout, though, Utah State made an extended 21-7 run, getting the deficit down to 58-54 on Drake Allen’s 3-pointer with 6:34 left.

“They amped up their pressure and their press, so I’m going to give them credit,” Arizona coach Tommy Lloyd said. “But our guys did a good job in there. You hang in there, hang in there. You have a little lead, you just need to make one or two plays in a timely fashion, and then you can kind of ride the game out.”

It was still a five-point game at 66-61 after an Allen basket with 3:56 to play, but 7-foot-2 Motiejus Krivas grabbed an offensive rebound, his fifth of the half and eighth of the game, and converted two free throws to make it 68-61.

Arizona’s lead was 70-64 when freshman guard Brayden Burries, who began the game with a 3-point shot from the top of the circle, basically ended it with another 3 from about the same spot with 2:18 left.

“Brayden’s 3 was pretty big time,” Lloyd said.

Said Calhoun: “I thought that 3 by him was just a big-time shot in a big moment.”

With Krivas leading the way with 14, Arizona more than doubled Utah State’s rebound total (54-26). The Wildcats also made more than triple the number of free throws (27-39 compared with 8-11).

Jaden Bradley led Arizona with 18 points despite a 1-for-9 shooting start while Burries — playing just 100 miles from where he went to high school in Eastvale — had 16 points and nine rebounds. Fellow freshman Koa Peat added 14 and 10. Krivas finished with 11 points and three blocked shots.

Garry Clark came off the bench to score 13 for Utah State, while Collins had 12 and Allen 11. But Collins made just 4 of 14 shots and Mason Falslev, the Mountain West Player of the Year, just 3 of 12 as he scored eight points. The Aggies finished 8 of 32 from 3-point range.