Tkachuk scored with 42.7 seconds left in the extra session, helping St. Louis rally from a one-goal deficit and beat the Blue Jackets 2-1, the Blues' second overtime victory over Columbus in five days.
Last Friday, Tkachuk helped set up Doug Weight's game-winner with 8.7 seconds left. His hit on Darryl Sydor gave the Blues a three-on-one break and left the Blue Jackets fuming about an obstruction penalty they didn't get.
"They got a tremendous effort from a tremendous player in the overtime," Columbus goalie Marc Denis said. "I would have loved to have made the save there."
Tkachuk scored his team-leading 16th goal after stopping Chris Pronger's shot short of the net. Lunging to his right, he pushed a backhand shot past Denis while falling.
"It was just one my typical bad skating, falling and getting lucky," Tkachuk said. "I was just there around the net because eventually the puck's going to be there."
The Blues have won their last four games by one goal, three in overtime.
"We're confident and we've been very successful in overtime," Tkachuk said. "It's just one of those things where you've got to ride the wave."
The Blue Jackets, who led 1-0 after two periods on a deflection by Andrew Cassels, remained the only NHL team without a road victory. They're 0-11-1-2 away from home this season and 0-12-1-2 dating to last season.
But they felt good about this one.
"It's games like tonight where you scrap and claw to get yourself a point, they're going to pay off down the stretch," center Todd Marchant said.
Dallas Drake added a power-play goal for the Blues at 6:46 of the third period, knocking in the rebound of a point shot by Alexander Khavanov. The Blues are unbeaten in December at 6-0-1, and they're 11-2-1-0 this season at the Savvis Center.
"We never do it the easy way," goalie Chris Osgood said. "But we find a way."
St. Louis missed a chance to end it in regulation after Derrick Walser was whistled for a double-minor for high sticking on Mike Danton. Denis stopped shots from Christian Backman, Eric Nikulas and Pavol Demitra in the final 1:30 of the third.
The Blues had a 17-10 advantage in shots in the second period, but the Blue Jackets got the only goal. Andrew Cassels got his fifth goal with a deflection of a drive from Walser on a power play at 11:19.
It was only the third power-play goal allowed by the Blues at home in 57 chances. St. Louis entered the game with the NHL's best home penalty-kill unit. The Blues have allowed just two power-play goals in the last eight games overall.
The Blues missed a chance to tie it when Denis stopped Demitra on a penalty shot at 18:12 of the second. The shot was awarded after David Vyborny pushed a stick into the path of the puck, knocking it out of the Blue Jackets' zone, during a St. Louis power play.