Two of Toews's trio of scores came in the three-goal Chicago third period, which began with Senators leading 4-3.
Toews tied the score at 1:20 and then staked the Blackhawks to a 5-4 lead with a backhander at 9:13. Andrew Shaw's goal at 11:14 proved to be the game winner.
Marian Hossa chipped in with a goal and two assists for the Blackhawks, who have won four of their last six games. Corey Crawford replaced Nikolai Khabibulin in goal in the second period and fended off all but one of the 15 shots he faced.
Ottawa's Craig Anderson gave up six goals on 40 shots. The Senators lost their third game in a row.
Kyle Turris and Milan Michalek both posted a goal and an assist for the Senators. Zack Smith scored a late goal in the third period that cut Chicago's lead to 6-5. Ottawa pulled Anderson in the final minute and mounted a furious charge with an extra skater, but Crawford stood up to the challenge.