AIR FORCE ACADEMY, Colo. (AP) -Utah tailbacks Darrell Mack and Matt Asiata have cast ego aside, never complaining about having to split carries.

Together, they provide a powerful one-two punch. And on Saturday, they were the main reasons the Utes stayed unbeaten.

Asiata rushed for 116 yards and Mack scored three second-half touchdowns, including a 9-yard run up the middle with 58 seconds remaining, to help No. 20 Utah rally for a 30-23 win over Air Force.

''They have both humbled themselves to help us,'' Utah quarterback Brian Johnson said. ''They've done an unbelievable job.''

Johnson's reliable running backs helped get him off the hook. The usually steady Johnson fumbled twice and threw an interception in the first half. He came into the locker room, with his team trailing, and asked his them to bail him out.

''I told them I'd get it corrected,'' said Johnson, who threw for 243 yards and a touchdown. ''I told them to keep the faith.''

Not that it ever wavered.

''We believe in what he says,'' said Mack, who finished with 101 yards on 18 carries. ''He's our leader.''

The Utes are off to a 4-0 start for the first time since 2004, when they went 12-0 in Urban Meyer's last season with the team before he bolted for Florida.

This victory wasn't exactly pretty, but that mattered little to the Utes.

''A sign of a good football team is when you don't play your best football and still get a win,'' Johnson said.

Utah (4-0, 2-0 Mountain West Conference) kept Air Force's vaunted ground game in check, allowing just 53 yards. The Falcons (3-1, 1-1) entered the game with the second-best rushing offense in the nation, averaging 358 yards a game.

''Our (run defense) was awesome,'' Utah coach Kyle Whittingham said. ''Fifty-three yards rushing for an Air Force team? That says it all. There's no further explanation needed.''

However, the Falcons got back into the game by discovering their passing game, something that was missing in a win over Houston the week before when quarterback Shea Smith went 0-for-7. It was only the fifth time in school history the team didn't complete a pass.

Smith showed poise in the pocket against the Utes, directing the Falcons to a game-tying score with 5:06 remaining. He completed a 37-yard pass to Kevin Fogler and then a 29-yarder to Josh Cousins , setting up Savier Stephens ' 1-yard touchdown plunge.

The nerves began to build about that time for the Utes - at least for Mack.

It didn't show as Utah methodically moved the ball down the field, even converting a long third down early in the drive. Mack then broke through the middle of the Air Force defense for the go-ahead score.

''This was a gut-check game for us,'' said Johnson, who was sacked five times. ''It's not always going to be as clean and perfect as you'd like. There's going to be some adversity. We battled through some things.''

Johnson was sacked by Rick Ricketts late in the second quarter, the ball squirting free. Jake Paulson picked it up and rumbled 25 yards for the touchdown, giving the Falcons a 16-9 lead at halftime.

''I wish I remember more about what happened. It was all kind of a blur,'' Paulson said. ''It was kind of a (defensive) lineman's dream. I suppose I should feel better, but given the circumstances, you've got to take it in stride.''

Air Force had scored just minutes earlier when Kyle Lumpkin hauled in an 8-yard touchdown pass from Smith. The touchdown was set up by a 42-yard catch by Fogler.

The Utes dominated the opening quarter, going up 9-0 on a 47-yard touchdown reception by David Reed down the left sideline, followed by a safety when Falcons punter Ryan Harrison fumbled the ball out of the end zone.

Air Force had minus-3 yards rushing in the first quarter.

''We've got to be completely cognizant of what we do as a football team. And if running it is something we do well, then that's what you may have to do a good bit,'' Air Force coach Troy Calhoun said. ''But Utah is really, really good. They are strong at every position. They have tremendous quickness. They are certainly a squad that deserves to be in the top 15.''