DaNarius McGhee's three-yard touchdown pass to Brain Flotkeotter gave Montana State the lead with 2:59 remaining, and Southern Utah's final drive ended with a tipped pass and interception in the end zone on the last play of the game.
Before the last-gasp drive, which carried the Thunderbirds from their own 10 to the Montana State 23, they squandered some tremendous field position.
Lamb called it the difference in the game.
Southern Utah's defense forced four turnovers including three in the final 17 minutes and three inside the Montana State 32-yard line.
But SUU's offense turned the Bobcats' mistakes into only seven points, and the Thunderbirds watched their record slip to 2-3 overall and 1-1 in conference play.
The game featured two of the league's top quarterbacks Brad Sorensen of Southern Utah and McGhee.
Neither was outstanding perhaps because of outstanding defense but McGhee was more effective down the stretch.
With the score tied 17-17, Southern Utah recovered a fumble at the Montana State 32 with eight minutes left. The Thunderbirds lost one yard during the next three plays, and Colton Cook missed a 50-yard field goal on fourth down.
Asked about the effectiveness of Montana State's defense, which limited SUU to 319 yards, Sorensen said, "It was nothing we weren't expecting. … They're just a good team."
After Cook's miss, Montana State drove 68 yards for the go-ahead touchdown. McGhee made a huge play when, on third-and-10 near midfield, he scrambled for 20 yards.
"That quarterback operates that offense in a slick fashion," Lamb said.
Montana State moved to the 3-yard line, where, on another third-down play, McGhee rolled out and hit Flotkoetter for a touchdown that made it 24-17.
Southern Utah had 2:59 to tie the game and nearly succeeded, but Sorensen's final pass to Mitch Jessop was tipped and picked off.
"Brad threw it up and gave me a chance to go get it," Jessop said. "I could feel the defense coming down. ... It was a just a jump ball."
R Second-ranked Montana State scores with 2:59 left and holds off Southern Utah, 24-17.
• The Thunderbirds force four turnovers but turn them into only seven points.
• A crowd of 8,417 attends the first Big Sky Conference home game in SUU history.