Ihemelu scored from inside the top left corner of the box in the 95th minute, taking a nice setup from Zach Loyd on a free kick from 25 yards out and heading it into the right corner.
The win snapped a three-game winless streak for FC Dallas (2-2-1), while New England (2-3-0) failed to win three straight games for the first time since August 2009.
Dallas goalkeeper Kevin Hartman finished with three saves.
New England keeper Matt Reis made two stops in the final 10 minutes, stopping a close- range shot from Fabian Castillo in the 91st minute and leaping to punch away Brek Shea's right-footed volley from the top of the penalty box in the 87th. Reis finished with five saves.
- New England Revolution
- FC Dallas
- Ugo Ihemelu