Midfielder Dax McCarty, left, was left unprotected by FC Dallas in the expansion draft, selected by Portland, then traded to D.C., where he is team captain. He looks forward to Saturday’s match against his former team. (Richard A. Lipski/For The Washington Post)

During D.C. United’s video session Friday morning, captain Dax McCarty was more talkative and animated than usual. McCarty, a 5-foot-7 feisty midfielder, is always a bundle of energy, but with his former club, FC Dallas, in town for Saturday’s match, his anticipation was heightened.

“He was very chatty because he knows everything about them,” teammate Chris Pontius said. “He knows how to break them down, which is good for us. He knows what makes them work. I know he wants to go out and perform well.”

McCarty, 24, started 71 regular season matches in five seasons with Dallas and, last fall, played an essential role in the club’s first appearance in MLS Cup. The day after the 2-1 overtime loss to the Colorado Rapids, however, Dallas declined to protect him from selection in the expansion draft — a decision that surprised many around the league, including McCarty.

“It will be a strange feeling,” he said of Saturday’s reunion at RFK Stadium. “They’re good friends of mine, like brothers to me. I’m looking forward to it, more than anything. It will be fun to see them, but once we step on the field, it’s all business and you have no friends.”

McCarty had worked in Dallas’s engine room, winning the ball with relentless pursuit and grit. But three days after the emotional final in Toronto, the Portland Timbers selected him with the first overall pick in a draft that also supplied players to the Vancouver Whitecaps.

McCarty had just landed in his native Orlando for a Thanksgiving family gathering when his father broke the news to him. Within an hour, though, United Coach Ben Olsen and General Manager Dave Kasper were calling to say they’d acquired him and financial considerations from the Timbers in a trade for defender Rodney Wallace and a fourth-round draft pick.

“It was a little bit of a surprise, a little bit of a shock, but as soon as that sinks in, you’re ready to take the next step in your career,” he said of being exposed in the expansion draft. Each team protected 11 senior players.

“As soon as I found out I was coming to D.C., I couldn’t have been happier because ultimately I get to play for a coach who I feel not only wants to take me to the next level, but wants to take this team back to where they need to be, which is competing for MLS Cup every year.”

Olsen began lobbying the front office to acquire McCarty while still in limbo as the interim coach. In McCarty, he saw himself — an industrious, resourceful player with strong leadership qualities and the flexibility to transition between defense and attack.

Despite McCarty’s recent arrival, Olsen bestowed him the captain’s armband. The previous holder was Jaime Moreno, the league’s career scoring leader who retired over the winter after 15 MLS seasons.

Pontius and McCarty are the only D.C. players to start each of the eight league matches. Like most of his teammates, McCarty didn’t perform well in several early matches, culminating with a 4-1 loss at Houston last week. But he was back in form Wednesday, when United (3-4-1) ended a two-game skid as well as Seattle’s six-game unbeaten streak with a 2-1 victory.

After a quick turnaround, McCarty’s attention is affixed on his former employer (3-3-1).

“I have tremendous respect for that organization,” said McCarty, who turned pro after two seasons at the University of North Carolina, was a 2008 Olympian and has received periodic national team call-ups.

“They gave me my first chance to be a professional, so they’ll always have a special place in my heart. But D.C. is my team now — that’s who I fight for and that’s who I want to win for. It’s a special game, but if we don’t come out with three points, I’ll be very, very upset.”

United notes: Pontius (calf), Clyde Simms (calf) and Marc Burch (hamstring) will likely be available, Olsen said. Burch sat out Wednesday while Pontius and Simms came off in the second half. Kurt Morsink (concussion) remains sidelined. . . .

Last weekend, Dallas defeated the Los Angeles Galaxy, 2-1, in its first match without playmaking midfielder David Ferreira, the 2010 league MVP who is nursing a broken ankle. . . .

Moreno, who accepted a job in United’s youth program this spring, will guide the newly created under-23 squad, which will play MLS reserve teams and amateur sides from the fourth-division Premier Development League.