Guerin also scored at 9:28 of the third to send the contest into the overtime.
Ryan Johnson scored the game's first goal in the first period; Christian Backman had two assists; and Manny Legace made 21 saves on 23 shots for the Blues, who have won three in a row following an 11-game losing streak.
Jochen Hecht and Jason Pominville each scored once; Daniel Briere assisted on both goals; and Martin Biron was beaten three times on 32 shots for the Sabres, who have lost three of their last four games.
On the power play, Buffalo went 0-for-3; and St. Louis was 0-for-2.
Hecht's goal was the 100th of his career.