The Blues have lost all three meetings with the Canucks this season and Lack has allowed just three goals in the three games.
St. Louis has not scored a power-play goal in four consecutive games. The Blues are 0 for 21 on the power play in those contests.
Halak stopped 34 of the 35 shots he faced Wednesday, but it was the lone goal from Jannik Hansen at the 11:13 mark in the third period on a partial breakaway that made the difference.
Halak is now 1-2-1 in his last four starts, though he has a .933 save percentage (stopping 125 of 134 shots) during that stretch. It will be interesting to see if Ken Hitchcock goes back to Halak for Friday's showdown in Anaheim or whether he gives Brian Elliott the start.
Hitchcock had some unusual line pairings for the Blues' first game back after the break.
He moved Patrik Berglund, who was coming off a strong Olympics with Sweden, to left wing on the first line with U.S. Olympians David Backes and T.J. Oshie.
Berglund's Swedish teammate, Alexander Steen, had been a fixture with Backes as a winger on that first line but was moved to the second line, where he was the center for wingers Chris Stewart and Jaden Schwartz.
Late in the third period, when they were chasing the game-tying goal, the Blues reunited Backes, Steen and Oshie on the top line. That is the trio that had carried St. Louis at times during the early portion of the schedule before Steen missed time with a concussion.
Like the goaltender situation, Hitchcock's handling of the lines Friday against the Western Conference-leading Ducks will be a key development to watch.