Bailey scored a power-play goal in the first period, and assisted on the winning goal from Casey Cizikas midway through the third, when he outwaited Senators goaltender Craig Anderson and slid the puck into the crease from behind the goal-line for Cizikas.
The win was the third straight and fifth in six games for the Islanders (31-35-10), who got a 35-save performance from rookie Anders Nilsson.
Ryan Strome chipped in with two assists.
Milan Michalek scored the lone goal for the Senators (32-30-14), on the power play 6:41 into the third period.
Michalek was at the side of the Islanders goal when he jammed a loose puck past Nilsson with four bodies lying in the crease.
The loss snapped a three game winning streak for the Senators. They had also recorded points in five straight games going into Wednesday.
Bailey had the only goal through 40 minutes of play, beating Anderson with a snap shot from the face-off circle 17 minutes into the first period.
The Senators had managed to kill off a 34 second five-on-three disadvantage but were unable to escape the back end of the two penalties unscathed.
It wasn't the only opportunity on special teams for the Islanders, either. Cal Clutterbuck was unable to cash in on three short-handed opportunities.
Clutterbuck was stopped by Anderson on a short-handed breakaway early in the first period, and later in the period, with an open net to shoot at, he slid the puck through the crease and along the goal-line.
Clutterbuck had another short-handed breakaway, this time in the dying seconds of the third period, but his shot sailed over the Ottawa net.
Notes: Defenceman Jared Cowen and forwards Bobby Ryan, Jason Spezza and Colin Greening are all injured and did not play Wednesday for the Senators. Defencemen Radek Martinek, Lubomir Vishnovsky and Brian Strait and forwards Kyle Okposo, Eric Boulton and Michael Grabner did not play for the Islanders … The Senators have not won five straight this season … The Senators close out a five-game homestand Friday when the host the Montreal Canadiens … The Islanders are 13-4-2 in their past 20 road games … Wednesday was the 400th game in the career of Islanders forward Josh Bailey.