New York, Montreal, Houston and Kansas City all began the evening's action with 17 points, tied for the top in the conference.
Houston kept pace with New York by routing D.C. United 4-0.
Henry scored just before the end of the first half and added a goal in 88th minute, that one coming in spectacular fashion on an overhead kick that beat goalkeeper Troy Perkins.
Luis Robles scored for Montreal in the 90th minute, but the Impact could not prevent New York from its fourth consecutive victory.
New York improved to 6-4-2 while Montreal slipped to 5-2-2.