If Union fans didn't know the name 'Nelson Rivas' prior to Saturday night, they'll know about him afterward.

Rivas committed one of the most-egregious fouls against the Union in their three-year history, head-butting Antoine Hoppenot above the right eye in the 68th minute of the Montreal Impact's 2-0 victory at Stade Saputo.

In a match that should have been entertaining for different reasons -- with the Union (7-11-2, 23 points) and the Impact (9-13-3, 30 points) jockeying for position in the Eastern Conference table -- it was instead marred by Rivas' foul. Rivas got red-carded, and is likely to get suspended and fined handily by the MLS disciplinary committee for his part, as did the Union's Jack McInerney, who was sent off for shoving Rivas to the ground in retaliation.

"In the 68th minute, we should be up a man," Union manager John Hackworth said.

There's no question. If you haven't yet seen the play, watch it in the video above. Hoppenot and Rivas get their arms tangled while contending for a ball in the air, with Hoppenot slinging Rivas to the ground. Rivas bounces up from the turf, stalks toward Hoppenot and delivers a head-butt to the Union rookie, sending Hoppenot to the ground. McInerney, who was only a few yards away, races in to shove away Rivas and point in Rivas' face while he's sprawled on the turf.

While the Union would much rather have McInerney in their lineup than on their bench next weekend, when they face the Chicago Fire Aug. 12 at PPL Park, McInerney's one-game suspension for his red card is forgivable. He's doing what he's supposed to do, to support an injured teammate.

"Rivas made a foul and that was obvious that he was getting a red card," Union captain Carlos Valdes said. "We made a mistake, when we came to him and tried to create a big problem. I think we’ll have to learn all these things."