Battaglia hasn't played in the NHL since he finished the 2003-04 season with the Washington Capitals. The 30-year-old winger spent all of last season in the American Hockey League with the Leafs' affiliate, the Toronto Marlies.
He and O'Neill played for new Leafs coach Paul Maurice in Carolina and Maurice reunited the pair, along with John Pohl, and Toronto rebounded from a 4-0 loss in its exhibition opener to the Buffalo Sabres on Monday to record its first victory of the pre-season.
After Mike Fisher broke a scoreless tie for Ottawa in the second period, O'Neill stripped Senators defenceman Chris Phillips of the puck and fed Battaglia on a 2-on-1 break to even the score.