Marian Hossa and Ben Smith also scored for the defending Stanley Cup champions, who have won three in a row and can wrap up the first-round series at home Sunday. Four of the first five games in the series have gone to overtime.
T.J. Oshie and Alex Pietrangelo scored for the Blues.
All three of the Blues' home games went to overtime and St. Louis won the first two. Toews got behind the St. Louis defense on the winner and threw a couple of fakes at goalie Ryan Miller before slipping the puck past him.
Before Toews scored, the top offensive threats in the series had been neutralized during Game 5. Chicago's Patrick Kane and Toews combined for one assist in regulation and the Blues' Vladimir Tarasenko, who entered with an NHL-leading four goals in the playoffs, was held to two shots.
The four goals in regulation came from players scoring for the first time in the series.
David Backes returned for the Blues while Blackhawks defenseman Brent Seabrook finished a three-game suspension from the illegal hit that knocked the St. Louis captain woozy in Game 2. But the Blues didn't make the most of that emotional lift early, getting their first scoring chance at about the 12-minute mark, totaling one shot on two early power plays and trailing 1-0 after the first.
At Philadelphia 2, New York 1: Steve Mason stopped 37 shots in his first start of the series, Matt Read and Jakub Voracek scored and the Flyers evened their first-round matchup against the Rangers with the Game 4 win.
Ray Emery started the first three games for Mason, who was out with an upper-body injury. Mason played the final 7:15 in a 4-1 loss Tuesday night.
Dominic Moore scored for the Rangers.
Game 5 is Sunday at Madison Square Garden.