Ian Book completed 22 of 34 passes for 343 yards and two touchdowns, and No. 4 Notre Dame held on for a 31-21 win over Northwestern on Saturday night at Ryan Field in Evanston, Ill.

Book and Dexter Williams each rushed for a score for Notre Dame while Miles Boykin and Michael Young hauled in touchdown passes. The Fighting Irish (9-0) have three games to go in their quest for a perfect regular season and a spot in the College Football Playoff.

Clayton Thorson completed 16 of 29 passes for 141 yards and one touchdown for the Wildcats (5-4), who were trying to beat a ranked opponent for the third time in a row. Thorson also rushed for a pair of touchdowns.

Notre Dame led 24-7 early in the fourth quarter before Northwestern scored back-to-back touchdowns to pull within 24-21. Thorson fired a 27-yard scoring pass to Riley Lees with 11:16 to go in the fourth quarter, and he brought the Wildcats within three points when he pushed across the goal line from 1 yard out on fourth-and-goal with 7:05 remaining.

The Fighting Irish sealed the victory with Book's 23-yard rushing touchdown on the next possession.

For a while, it looked as if Notre Dame would not have to worry about the final few minutes. A 43-yard field goal by senior kicker Justin Yoon put the Fighting Irish on top by 17 points with 13:05 remaining in the fourth quarter.

Yoon's kick followed a pair of touchdown passes by Book. The junior signal-caller lofted a 20-yard touchdown pass to Boykin with 7:28 to go in the third quarter, and he fired a 47-yard strike to Young later in the quarter for another score. Young caught the pass over the middle of the field and sprinted to the end zone for his first touchdown of the season.

Northwestern battled back with 14 points in a 4:11 span.

The score was tied at 7 at halftime.

Notre Dame opened the scoring with 6:28 remaining in the first quarter. Williams punched across the goal line from 1 yard out for his eighth rushing touchdown in five games.

Northwestern evened the score at 7 on Thorson's 1-yard sneak with 8:04 left in the second quarter.

--Field Level Media