This was one of 4 straight games in that year's tournament where this UNLV team played "good" but not close to the standard they had set throughout the season. They normally won by Dream Team-like scores, even against top non-conference teams. But in this tournament they just won in workmanlike fashion and did not resemble the intimidating juggernaut they had been. Came back to bite them in the next game.
Duno, they won their first game our the tourney by 34 against Montana or someone like that, their largest MOV of all their wins in that 1990-91 10 game streak.
Complacency definitely set in. After beating the brakes of Arkansas at their place, maybe not much left to prove? After scoring over 100 points 3 times in the '90 tournament, they didn't break 100 once during the '91 tourney. As you eloquently stated, they relied on big 2nd half runs to get by, and that never came in the next game.