Fourth-ranked Notre Dame’s much-maligned defense allowed it to overcome some red-zone struggles on Saturday afternoon as it posted a 12-7 victory against Louisville in ACC play at South Bend, Ind.Quarterback Ian Book scored the lone touchdown on a 13-yard scramble as the Irish (4-0, 3-0 ACC) held on against the Cardinals (1-4, 0-4).Book passed for 107 yards and rushed for 47 yards. Kyren Williams rushed for 127 yards on 25 carries, including a 24-yard run late in the fourth quarter that allowed the Irish to run out the clock and secure the win.A week after allowing 405 yards in a 42-26 win over Florida State, the Irish limited Louisville to just 234 total yards, and held Louisville’s Malik Cunningham to 134 passing yards. The Cardinals suffered their fourth straight loss.Cunningham put Louisville up 7-6 on a 1-yard touchdowns pass to tight end Marshon Ford with 7:37 left in the third quarter, but Notre Dame answered with an eight-play, 66-yard touchdown drive, capped by Book’s 13-yard run to go back up 12-7.Notre Dame failed to reach the end zone in three trips inside the red zone in the first half, scoring just six points on a pair of field goals. The Irish settled for a 32-yard Jonathan Doerer field goal after driving 61 yards on 12 plays to Louisville’s 14-yard line to open the game. A 30-yard field goal by Doerer later in the first quarter put the Irish up 6-0.