Cristobal Huet made 27 saves in the setback for the Blackhawks (25-12-8), who have dropped three of four heading into the schedule stoppage.
The visitors squandered an early five-minute power play as Hawks defenseman Cam Barker took down Blues forward David Backes with a questionable hit and was given a major for interference.
After amassing a 16-3 shot advantage through the opening 20 minutes, the Blues eventually took a 1-0 lead on a late man advantage on a Woywitka blast that trickled through Huet's pads with 1:55 left in the first.
Mason was only tested six times in the second period and stopped all the chances.
Tkachuk gave St. Louis a two-goal edge 7:28 into the third period, and Mason kept the Hawks off the board with a 12-save effort.