With Heisman hopeful quarterback Dan Persa confined to the sidelines with a nagging Achilles tendon injury, Northwestern struggled to convert crucial third-down plays as Army (1-2) topped the Wildcats 21-14 Saturday.
The defeat broke a streak of seven straight regular season nonconference victories for Northwestern (2-1), part of a larger 14-1 stretch.
Backup QB Kain Colter got the start but was pulled in the fourth quarter in favor of Trevor Siemian. Colter finished with 89 yards on 12-of-23 passing, including a 14-yard touchdown pass to Jeremy Ebert late in the first half to tie the game at 7-all.
That proved to be Northwestern's last points for nearly two full quarters until Siemian (105 yards) connected with Ebert for a 62-yard strike to tie it at 14 with 6:03 to go in the fourth.
''I 100 percent feel like it was my fault,'' said Colter, a sophomore who added a team-high 57 rushing yards. ''I didn't put points on the board, didn't help my team out, and I take the blame for that. I just had a terrible game and let my team down.''
The Wildcats were 3-of-12 on third downs and had possession for 19:41, a third of the game, taxing both sides of the ball.
''We had to be in hurry-up offense all the time,'' Wildcats coach Pat Fitzgerald said. ''We had to step out and do something completely different than we usually do.''
Northwestern, whistled for seven penalties for 60 yards, also fell 23-7 in 1988, Army's last Big Ten opponent at Michie Stadium.
Trent Steelman scored three touchdowns for the second straight week, including the game-winner on a 1-yard plunge with 2:49 remaining, to lead Army. Steelman also scored on runs of 1 and 17 yards, and the swarming Army defense turned up the pressure in the second half.
Malcolm Brown had a 23-yard gain on a pitch right for Army (1-2), Raymond Maples added a 17-yard run off a great fake in the middle of the line, and Scott Williams had a 17-yard run around the left side to key the game-winning drive. Steelman converted a third-and-6 play from the 9 and scored two plays later.
The Wildcats had one last chance to tie, and Siemian hit Ebert for 18 yards into Army territory. But the Army defense forced an incompletion of fourth down with 66 seconds left.
Ebert also had a 14-yard touchdown catch in the second quarter from Colter.
Persa warmed up before the game and had a headset on during the action. He's expected to return Oct. 1 when Northwestern opens Big Ten action against Illinois.
Army finished with 381 yards rushing on 75 carries to Northwestern's 115 yards on 27 tries. The teams entered the game ranked 1-2 nationally in total number of rushes.
While losing its first two games to Northern Illinois and San Diego State, Army turned the ball over three times in each and was a minus-2 per game in turnover margin. Steelman had two more fumbles against the Wildcats, losing one. But neither cost the Black Knights this time, thanks to a defense that held Northwestern to 10 yards offensively in the third quarter and 117 in the second half - including 62 on the play that tied the game.
Siemian, a redshirt freshman, replaced Colter after Army's Alex Carlton missed a 26-yard field goal just past the midway point of the fourth quarter, and the Wildcats scored in just three plays. The third was a short dump to Ebert, and he outran the only defender that had a chance to knot the score at 14 with 6:03 left.
Steelman lost the handle after a snap early in the second quarter and quickly pounced on it, but he wasn't so lucky midway through the third. He again mishandled a handoff, and linebacker Ben Johnson recovered for Northwestern at the Army 30.
The Army defense forced two incompletions, and a sack by Army linebacker Steven Erzinger allowed the Black Knights to escape.
Army's triple option thrives on ball control - the Black Knights entered the game ranked second nationally in rushing, averaging 353 yards, and second in possession time, averaging 37 minutes, 35 seconds - and it couldn't have operated much better than on their first possession of the game.
After forcing the Wildcats to punt, Army marched 81 yards on 18 plays on a drive that lasted nearly 9 minutes. Steelman had seven carries for 49 yards, including a 6-yard run left on a fourth-and-5 play from the Northwestern 38-yard line and scored on a pretty 17-yard scamper around the left side with 3:39 left in the opening quarter.
It was the first time Army had led this season.