The victory made the Titans 5-0 and continued the best start in franchise history.
The game-winning scoring pass covered 11 yards with 1:56 remaining, erasing a 10-6 deficit and finishing an 80-yard drive.
Collins completed 17-of-32 passes for 163 yards and overcame two interceptions.
Bo Scaife made seven receptions for 72 yards and Titans placekicker Rob Bironas hit both his field goal attempts.
Baltimore rookie quarterback Joe Flacco was 18-for-28 passing for 153 yards with two interceptions.
Fullback Le'Ron McClain scored the lone touchdown on a 1-yard third quarter run. He gained 51 yards on 11 carries.
Willis McGahee ran for 64 yards on 22 carries and Todd Heap caught four passes for 41 yards for the Ravens (2-2), who have lost two in a row after two straight season-opening wins.