Locker, the Titans' eighth-overall pick in the 2011 NFL draft, stepped in after Matt Hasselbeck played in the first series and tossed for 89 yards.
His best play came in the second quarter when he fumbled the snap, picked it up and found Yamon Figurs for a 45-yard touchdown pass.
Jamie Harper, another Tennessee rookie, rushed for 27 yards and a TD.
Veteran signal-caller Donovan McNabb made his debut for the Vikings and played two series, tossing for 40 yards in a 6-of-11 performance.
First-round draft pick Christian Ponder entered the game in the second half and went 8-for-13 for 84 yards.