Vrbata and Mikael Holmqvist also scored in regulation for the Blackhawks, who snapped a three-game losing streak. Chicago's Patrick Lalime, who played five seasons with Ottawa from 1999 to 2004, blocked 30 shots.
Chicago's Brent Seabrook scored on a screened shot from the left point during a 4-on-4 with 1:59 left in the third period to set up overtime, as Chicago rallied from a 3-1 deficit.
Daniel Alfredsson had a goal and an assist for the Senators, who lost their second straight.
Oleg Saprykin and Antoine Vermette also scored for Ottawa, which got 22 saves from Martin Gerber.
Dany Heatley and Jason Spezza both extended their point-scoring streaks to 11 games when they assisted on Alfredsson's power-play goal early in the second.
Heatley scored in the shootout for Ottawa but his goal-scoring streak ended at six games, as he failed to connect in regulation. He had scored eight times during the stretch.