Tempers flared during the Impact's 4-2 victory on Saturday night, which featured Patrice Bernier's goal on a penalty after Felipe Martins went down a little easily from a shove in the area. Houston's Adam Moffat was shown the red card moments later for taking the Brazilian midifielder down hard.
The incident in the 73rd minute caused a heated exchange of words between the teams on the field before play resumed without any further incidents.
"He's like our little brother," defender Zarek Valentin said of Felipe. "I know Moffat. He's not necessarily a dirty player. But we've got to protect his back. It's intimidation."
Hassoun Camara, Sanna Nyassi and Davy Arnaud also scored for Montreal (5-8-3), which is 2-0 in revamped and expanded Saputo Stadium after a 4-1 win over Seattle last week. They will try for three wins in a row when another rival, Toronto FC, visits on Wednesday for the MLS debut of Impact designated player Marco Di Vaio.
Will Bruin, with his ninth of the season, and Brad Davis scored for Houston (5-5-5) while former Impact forward Brian Ching, who was booed each time he touched the ball, had an assist.
Ching shrugged off the booing, which was loudest when he was substituted with nine minutes left to play, but he was not happy with the result or with the Impact. The Eastern Conference teams face each other twice more this season, both times in Houston on July 21 and Oct. 6.
"We'll be at home," said Ching. "They will be a lot different games.
"They're definitely not going to score four goals on us again, I can tell you that."
Ching also called for Impact technical director Nick De Santis to be reprimanded by the league for allegedly berating Moffat as he left the pitch and went to the team dressing room after his ejection. De Santis denied that ever happened.
"It's inexcusable from someone in his position," Ching added. "A red card, the guy made a mistake, got set off, they're up 4-2.
"You shouldn't have someone in their front office berating our player as he walks to the locker room. I think that's unsportsmanlike and it's something we'll remember when they come and visit us."
The Impact made Ching the first pick in the expansion draft in November, but the Dynamo captain was unhappy to leave the team he won two championships with and where he was captain. His request to return to Houston was granted in February when he was dealt for a conditional 2013 draft pick.
The Dynamo are one of MLS's best and most physical teams. They did well to battle back twice from one-goal deficits in the first half, but Montreal were all over them in the second to earn the three points.
Coach Jesse Marsch said his team "grew up" in the win. Valentin agreed.
"We grew some hair on our chests," said Valentin. "We needed a win like this.
"We were up against a tough team and they're know for being battlers. They played us tough, but we were able to get some goals going into Wednesday, which is a huge game."
Montreal had 16 shots, seven on target, while Houston attempted five and got three on Donovan Ricketts.
"Obviously, we love playing at home," said Valentin. "The fans urge us on and we get in a certain comfort level where we think goals will come."
For a second straight game, the Impact failed to sell out. The crowd was announced at 12,357, well short of the more than 19,000 capacity. But they were loud.
The Impact took the lead when Arnaud flicked a Felipe corner kick to Camara to score his first MLS goal with a header at the far post in the 60th minute.
Only eight minutes later, Felipe went down in the penalty area after a light shove from Geoff Cameron and a penalty kick was awarded, which Bernier converted.
In a busy first half Montreal took the lead twice before going into the intermission tied 2-2.
Only four minutes in, Bernier fed Felipe for a pass that split the defence to Nyassi, whose shot trickled past goalkeeper Tally Hall into the net.
Davis struck back in the 16th with a perfectly curled left-footed free kick from 22 yards that Donovan Ricketts couldn't reach.
Impact captain Arnaud, who turned 32 on Friday, headed in a Justin Mapp cross in the 21st, but with one minute left in the half, Ching slipped a pass behind the Montreal defence for Bruin to score.
Toronto has wasted two-goal leads and settled for draws in each of its last two matches, including a 3-3 tie in Houston on Wednesday.
Notes: Camara returned from a hamstring injury and started for Montreal in place of Shavar Thomas, while forward Sanna Nyassi replaced the injured Bernardo Corradi (torn ACL). Montreal was without defender Matteo Ferrari (thigh injury) and Andrew Wenger (hamstring) . . . . Houston had two changes, with Ching starting for Macoumba Kandji and Je-Vaughn Watson in for Luis Camargo. Defender Andre Hainault of Vaudreuil-Dorion, Que., played for Houston. The Canadian international began his pro career in Montreal in 2004.