After being stifled for much of the first half against Northwestern, the Hawkeyes rusher broke free for a spectacular 26-yard touchdown run to give his team a 12-7 lead just before halftime Saturday.
Johnson had just 4 yards on seven carries before breaking free.
The play also marked Iowa's first and only TD of the half. Iowa's offense struggled for much of the first two quarters, which forced a switch from starting quarterback Cade McNamara to backup Brendan Sullivan near the start of the second frame.