AIR FORCE ACADEMY, Colo. (AP) - Chance Harridge ran for four touchdowns for the second straight game, and No. 21 Air Force forced five turnovers as the Falcons beat Brigham Young 52-9 Saturday night.

Air Force (6-0, 3-0), the nation's top rushing team, had 463 yards - 386 rushing - and used its ball-control offense to keep BYU's high-scoring offense off the field. The Falcons are off to their best start since opening the 1997 season 7-0.

BYU (3-3, 0-1) couldn't get its offense on track and seemed baffled by Air Force's option in its conference opener. The Cougars entered the game averaging 441 yards, but had just 304 - minus-21 rushing - and used all four of its quarterbacks to lose for the first time in 10 conference games.

Harridge scored on a 1-yard sneak for Air Force's first touchdown, then put the Falcons up 14-3 late in the first quarter on a 4-yard touchdown run. He went in untouched on the second score after BYU's Kip Nielsen bit on a fake pitch on an option left.

Harridge again used a fake on an 11-yard touchdown run early in the second quarter, leaving Brandon Heaney standing near the 10 when he faked to the outside.

Harridge added a 1-yard dive on Air Force's first drive of the third quarter and finished with 104 yards on 22 carries. He had 161 yards and four touchdowns in a 48-7 victory over Navy last week.

BYU used an onside kick early to gain momentum in its 63-33 win over Air Force last year, but it was the Falcons turn this time.

Air Force tried the onside kick after Harridge's second touchdown, and Felix Cole recovered it at the Falcons' 47. Darnell Stephens followed with a 7-yard touchdown run around left end that put the Falcons up 21-3.

Leotis Palmer kept the drive going with a 16-yard run on fourth-and-1 from BYU's 44.

BYU rallied from a 27-point deficit last week against Utah State - the largest comeback in school history - but had no chance this time.

The Cougars tried a flea-flicker off a double reverse midway through the second quarter, but lost 22 yards when the pitch to quarterback Bret Engemann hit the ground. BYU also failed on fourth-and-3 from its 47 later in the drive when Marcus Whalen came up about an inch short of the marker on a run to the right.

BYU finally got its offense going late in the half, reaching Air Force's 6, but Engemann lost 6 yards when he tripped over right guard Quinn Christensen's foot, then lost a fumble when he dropped a snap at the 19.

Engemann had two passes intercepted, one by Anthony Schlegel that set up Harridge's third TD, and was just 10-of-22 for 143 yards.

Todd Mortensen replaced Engemann midway through the third, but threw an interception on his first pass and had two for the game.