Dwayne De Rosario, right, of D.C. United and Danny Cruz of the Philadelphia Union push each other at midfield during a preseason match at the Disney Pro Soccer Classic in Orlando. De Rosario was given a red card and sent off. (Al Messerschmidt/Getty Images)

With MLS openers a week away and players on edge after two months of hard practices and close quarters, D.C. United’s 2-0 preseason victory over the Philadelphia Union on Saturday turned into a predictably ornery affair.

Tackles were executed with extra force. Elbows were as prominent as feet. A searing sun at Disney’s sports complex added to the combustible brew for a game between teams with a history of foul behavior, clubs that had collided three days earlier.

In the 59th minute, tensions spilled over at midfield and United captain Dwayne De Rosario was ejected for allegedly head-butting former teammate Danny Cruz on the nose.

The incident began when Brian Carroll, another former D.C. player, grabbed De Rosario from behind. De Rosario turned and shoved Carroll, prompting Cruz to intercede. De Rosario could be seen cocking his head back as players swarmed on the scene.

“He elbowed Brian in the head and then he pushed him,” Cruz said. “So I came and pushed him away and he came up pretending like he was going to punch me and then head-butted me. It was a cheap shot.”

Cruz had a slight bruise across the bridge of his nose but wasn’t bloodied and didn’t require immediate treatment.

De Rosario declined an interview request.

“It’s a long preseason,” United Coach Ben Olsen said. “It’s chippy. People miss their beds and their wives, their kids, their girlfriends. We want to get the season going. It happens.”

Olsen added, “You watch the next game, it’s going to be the same thing.”

Right on cue, it did: In the second of four games at the Disney Pro Soccer Classic, Sporting Kansas City and Toronto FC exchanged shoves early and had an ejection in the second half.

Red cards during the regular season come with a one-game suspension, but because De Rosario’s ejection came in preseason, he will not receive an automatic ban for the March 2 opener at Houston. However, MLS’s disciplinary committee reviews such incidents and could impose sanctions.

The game was not televised or streamed online, though, and it’s unclear whether any definitive video of the incident exists.

De Rosario wasn’t the only player to receive a red card. Union goalkeeper Zac MacMath was penalized for upending Lionard Pajoy on a breakaway in the first half. De Rosario converted the penalty kick in the 38th minute.

Because it’s preseason and the teams want a full-strength experience, MacMath was allowed to continue playing. De Rosario had to depart because of the egregious nature and was replaced in the lineup to maintain even strength.

United (2-2-3 in preseason) added the second goal in the 67th minute when Panamanian trialist Marcos Sanchez set up Pajoy for his third goal in four tournament matches.

Olsen was pleased with his team’s fluid performance in the second half after an uninspiring start. Midfielder Perry Kitchen stood out, disrupting Union attacks and distributing the ball with confidence.

“The first half was a waste of time,” Olsen said. “We weren’t mentally prepared. I’ll take blame for that. Second half was good because we simplified the game, didn’t try to hit killer passes.

“We have to understand who we are. We are still not good enough — like we weren’t good enough last year — to step on the field and think we have done something. We haven’t. I hope we learned that lesson because if we do that in the first half against Houston, it’s going to be 2-0.”

Meantime, hostilities continued at the final whistle and players had to be separated.

“It is to be expected between our two clubs,” Cruz said. “There is a lot of bad blood and I think it’s a preview, hopefully, of the intensity that is going to come this year.”

The first of three regular season meetings is April 21 at RFK Stadium.

United notes: The club hopes to sign Sanchez, a right wing for Panama’s national team, in the next few days, Olsen said. Walter Martinez, a former Honduran national team attacker, was cut.