The Jaguars were clinging to a 22-20 lead with 2:32 left in the game when Blackmon stripped Tennessee quarterback Ryan Fitzpatrick of the ball and returned it 21 yards to secure the victory.
Maurice Jones-Drew and Jordan Todman each ran for a touchdown for Jacksonville (1-8), who took the lead on a fourth-quarter safety and held on to snap a 13-game losing streak stretching back to last season.
Fitzpatrick took over behind center for the injured Jake Locker in the first half and went 22-of-33 through the air for 264 yards with two touchdowns for the Titans (4-5).
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