The Tennessee Titans sustained a trio of key injuries in their opener against the Miami Dolphins, with quarterback Marcus Mariota, left tackle Taylor Lewan and tight end Delanie Walker all going down.Mariota hurt his elbow on a hit by William Hayes after handing off to Derrick Henry early in the third quarter. He was replaced by Blaine Gabbert and then returned, but he left the game again after throwing his second interception later in the third. Gabbert came back in, and Mariota did not return a second time.Lewan was ruled out with a concussion after taking a vicious, blind-side hit during an interception return early in the fourth quarter. The hit was not flagged.Walker went down with a gruesome injury to his right leg or ankle late in the fourth quarter after his foot was pinned underneath a defender while he was tackled. Trainers quickly tended to Walker and put the leg in an air cast before carting him off the field.Mariota, who missed five games over his first three seasons with various injuries, finished 9 of 16 for 103 yards and two interceptions. Gabbert went 11 of 22 for 117 yards and an interception as the Titans lost 27-20.