Jeff Budzien tied a school record with five field goals and the Wildcats (3-0) made it three wins over three BCS teams to start the season even though they didn't reach the end zone until the closing minutes.
They downed a punt at the 1 to pin Boston College (1-2) against the goal line and took over on the Eagles' 44 with 2:35 left in the game after they went three-and-out.
After going three quarters against Vanderbilt the previous week without a TD, Northwestern finally broke through in this one when Trumpy broke up the middle for a 27-yard scoring run that made it 22-13 with 1:37 remaining.
Before that, Budzien's leg provided all the scoring. Northwestern wasted several big chances, particularly in the early going, and had to settle for field goals instead of touchdowns. But with their kicker on target, the Wildcats led most of the way to come out with the win hours after the school announced plans for a new lakefront athletics complex that will include a facility for football.
Kain Colter threw for 144 yards and ran for 66, while Trevor Siemian threw for 123 yards. Venric Mark ran for 77 yards but spent the fourth quarter on the sideline limping with an undisclosed lower body injury.
Chase Rettig came up big for Boston College, completing 24 of 44 passes for 291 yards and a touchdown, but the Eagles fell short.
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Budzien's 41-yarder at the end of the second quarter gave the Wildcats a 12-10 lead, but that came right after another blown chance. A leaping Kyle Prater deflected a wobbly pass from Siemian in the end zone that probably should have been caught anyway for a 23-yard TD.
Northwestern caught a break after Colter lost a fumble near midfield on its first possession of the third quarter.
That led to a 19-yarder by Budzien to make it 15-10 late in the third, but again, the field goal came after a missed opportunity. This time, Colter overthrew a wide open Christian Jones in the end zone on second down at the 6 before getting stopped on a 4-yard run.
Nate Freese pulled Boston College within two with a 34-yard field goal in the opening seconds of the fourth.