Book finished the first half with just 63 passing yards, three sacks and a pair of fumbles, including one that was lost after he ran up the back of tight end Brock Wright.

And yet, after his ninth-ranked Fighting Irish had skated off with a 35-17 win before a record crowd at Cardinal Stadium, coach Brian Kelly went easy on his returning starter.

Book lamented the “sloppy football” he helped orchestrate in the first half, when Notre Dame fell into a 14-7 hole against a 20-point underdog coming off a 2-10 nightmare and a coaching change.

After a Louisville field goal made it a two-score game early in the fourth, Book engineered a 12-play, 75-yard scoring drive that included three straight third-down conversions.

Already without tight end Cole Kmet and third receiver Michael Young, both out following clavicle surgery, Notre Dame lost versatile running back Jafar Armstrong to a possible groin injury after three straight touches (for 26 yards) on a game-opening touchdown drive.

From Myron Tagavailoa-Amosa and Ade Ogundeji up front to middle linebacker Drew White to young cornerbacks TaRiq Bracy and Houston Griffith to freshman safety Kyle Hamilton (two pass breakups), the kids were more than all right on this night.