NASHVILLE, Tenn. (AP) Marcus Mariota had every reason to struggle on the first drive of his second preseason game when the communicator device in the Tennessee quarterback's helmet quit working.

Not a problem for the rookie.

Mariota turned in a clean performance in his home debut, Tennessee cornerback Perrish Cox returned an interception 24 yards for a touchdown and the Titans beat St. Louis 27-14 on Sunday night to spoil Rams coach Jeff Fisher's return to town.

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A week after Mariota was sacked, threw an interception and lost a fumble that was returned for a touchdown, the No. 2 pick overall out of Oregon was 5 of 8 for 58 yards with no turnovers. Titans teammate Dexter McCluster dropped Mariota's pass in the end zone, while Rams safety Mark Barron couldn't hold a would-be interception off the rookie.

''Most guys would panic at that point, but he handled himself like a pro,'' Titans coach Ken Whisenhunt said about Mariota's communicator device failing. ''He was calm. If we make two catches, he's got a touchdown and a big first down on that opening drive, so he played well.''

Tennessee's defense looked much improved against an offense that ranked 28th in the NFL last year. With Cox's interception, the Titans (1-1) finally stopped an opponent on the opening drive for the first time in six preseason games.

''That was kind of one of our goals as a defense,'' Cox said. ''As players, we have our own meetings about those kind of things, and that was one of the things that we wanted to come out and do since we didn't come out last week and start fast. Today that was the main goal, just come out and start fast, keep eating and keep the tempo up.''

Nick Foles had a rough outing in three series for the Rams (0-2).

He was 3 of 7 for 18 yards with the Rams going three-and-out on their next two series with the quarterback St. Louis brought to town in the trade that sent Sam Bradford to Philadelphia. Case Keenum found Chris Givens for an 80-yard TD toss in the third quarter to avoid the shutout, and Sean Mannion connected with Malcolm Brown for a 54-yard TD in the final minute.

That combined to make for an ugly return to a stadium Fisher helped open in 1999 when he coached the Titans to the Super Bowl that season where they lost to the Rams. Fisher, the winningest coach in Tennessee history after more than 15 seasons, was honored with a video tribute during the first timeout in the first quarter, and he acknowledged a standing ovation with a wave.

Mariota did drive the Titans to the first of two field goals by Ryan Succop in his three drives and left with a 10-0 lead. Zach Mettenberger continued his strong preseason and was 7 of 9 for 91 yards with a TD pass helping Tennessee lead 20-0 at halftime.

Tight end Chase Coffman, signed the day the Titans reported for training camp, scored two TDs on catches of 3 and 56 yards.

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Follow Teresa M. Walker at www.twitter.com/teresamwalker