Lack gave up four goals in regulation and overtime last Tuesday and then surrendered the only shootout score in a loss to Pittsburgh.
Against the Blues he surrendered only a second-period goal to Alex Pietrangelo and stopped 30 shots.
The score was tied 1-1 heading into the third period and Mike Santorelli produced the game-winner 5:53 into the stanza on a deflection.
Vancouver snapped a five-game skid.
St. Louis had not lost since falling in a shootout 4-3 at Calgary on Dec. 23. The Blues outscored the opposition by a combined 21-4 in the last four victories of the winning streak.
Brian Elliott suffered the setback, giving up two goals on 21 shots.