Guerin, coming off an appearance at the all-star game earlier in the week, scored his team-leading 21st goal as he gathered a rebound off the pads of Detroit goalie Chris Osgood and slapped it into the goal from about five feet away.
The teams traded goals less than two minutes apart midway through the second period.
Ryan Johnson returned to the ice after sitting out 12 games with a separated shoulder and notched his fifth goal of the season eight minutes into the second period. Jamal Meyers carried the puck deep into Detroit territory before wristing a shot at Osgood. The rebounded landed at Johnson's feet and he slipped it past Osgood to give the Blues a 1-0 lead.
It lasted 1:56 before Detroit's Johan Franzen tied the score. St. Louis defencemen Jamie Rivers and Dennis Wideman went to clear the puck just in front of the net only to hit sticks and leave the puck for Franzen, who beat Manny Legace for his sixth goal.