D.C. United midfielder Branko Boskovic, left, trips up Sporting K.C. defender Julio Cesar during the clubs’ MLS season opener on Saturday night at RFK Stadium. Kansas City won, 1-0, on C.J. Sapong’s goal in the third minute of added time. (Toni L. Sandys/The Washington Post)

D.C. United presented a fresh look for its MLS season opener on Saturday night, blending a proven European scorer with the reigning league most valuable player and two key attackers returning from long-term injuries. But United sputtered throughout the cool evening, and when Sporting Kansas City’s C.J. Sapong scored in added time, the 1-0 loss felt eerily similar to the late-season collapse last year.

United lacked cohesion and style, failing to test goalkeeper Jimmy Nielsen in front of 16,314 at RFK Stadium.

Bill Hamid’s quality saves kept the game scoreless until the third of four extra minutes, when Sapong, a Forest Park High School graduate and the 2011 MLS rookie of the year, found a pocket of space on Graham Zusi’s corner kick and nodded a seven-yard header into the left side.

In the days approaching the match, United Coach Ben Olsen tempered expectations, citing the lack of quality time together for the first unit. The group was slated to play in the preseason finale last weekend in Charleston, S.C., but a thunderstorm forced a cancellation.

“It wasn’t the greatest night for us, but I kind of knew it wasn’t going to be,” Olsen said. “It was the first time we’ve stepped on the field for a 90-minute game [with the primary players]. It’s not an excuse; it’s just the reality. So we were a little rusty, physically and mentally.

The ideas were right, but the execution was off. Albanian striker Hamdi Salihi, a late signing, and MVP Dwayne De Rosario were non-threatening. A minor groin injury had hindered De Rosario’s preseason preparations and Salihi didn’t receive a consistent supply of service.

Branko Boskovic, the playmaker returning from major knee surgery, displayed a rusty touch. Left wing Chris Pontius, back from a broken leg, showed promise but faded. Andy Najar was quick and tricky on the right flank but crossed poorly.

“It takes a lot of time getting to know players’ runs and where they want the ball,” Pontius said. “I don’t expect it to be clicking next game. There are going to be times where it’s looking good, and there are times where it’s going to look off. That’s all a process of figuring things out.

Late in the first half, Pontius worked a combination with De Rosario and surged into the heart of Kansas City’s defense for a 22-yard effort that skidded wide. It proved to be United’s best opportunity of the match.

Returning most of the lineup from a first-place finish in the Eastern Conference, Kansas City grew stronger as the game unfolded. It sounded a warning in the 45th minute when Kei Kamara’s six-yard header forced Hamid into an excellent foot save.

Kansas City continued to gain traction after halftime, utilizing speed to open the attack and run at the defenders. United found itself under growing duress, but Hamid made solid saves on bids by Zusi (University of Maryland) and Roger Espinoza.

United, meantime, was gassed.

“We looked a little tired toward the end of the game,” said Olsen, who replaced Boskovic, Pontius and Salihi in a 14-minute span. The entrance of Josh Wolff and newcomers Danny Cruz and Maicon Santos didn’t provide any answers.

“We realize we’ve got to be better late in the game,” said Robbie Russell, United’s new right back. “It’s the first game of the season and it’s a process.”

United notes: Club officials signed a new lease with stadium management, a long-anticipated agreement that will keep the club at RFK while it continues pursuing a project for a new facility in the city.

In a pregame interview, owner Will Chang seemed optimistic about the prospects of a new stadium . Chang confirmed Buzzard Point, near Nationals Park, is the club’s favored location. He said the RFK campus hasn’t been ruled out.

“Discussions are moving forward,” he said. “I appreciate what the city has done in support of the club and I feel good the city is very interested in wanting to keep us in the District.”