In one of the greatest accomplishments in American professional soccer history, D.C. United shocked Brazilian giant Vasco da Gama, 2-0, tonight at Lockhart Stadium to win the InterAmerican Cup club championship of North and South America.

Vasco, the world's second-ranked professional club, won the opener of the two-game series, 1-0, three weeks ago at RFK Stadium. That meant United, in just its third season, had to win by two goals tonight to claim the title or by one to force a 30-minute sudden-death overtime.

Midfielder Tony Sanneh gave United a 1-0 lead with a sliding goal in the 34th minute. Then, with about 13 minutes remaining and United hoping just to withstand Vasco's mighty charge and force the extra period, defender Eddie Pope knocked in Roy Lassiter's crossing volley off Marco Etcheverry's corner kick for the winning margin.

"This is an almost unbelievable accomplishment," an emotional Bruce Arena said following his final game as United coach before taking over the U.S. men's national team. "We beat one of the great clubs in the world. I'm very proud for D.C. United, I'm very proud for MLS and for soccer in the United States."

When referee Carlos Batres sounded the final whistle, United's players and coaches danced around the field as Vasco's players watched in amazed silence. A few dozen United supporters chanted, "We want Real! We want Real!" in reference to European champion Real Madrid, which defeated Vasco, 2-1, in the world club championship Tuesday in Tokyo.

"The cup is good for them," Vasco Coach Antonio Lopes said. "They played better than Vasco. The cup will be in good hands."

Although United lost in the Major League Soccer championship game six weeks ago, ending its two-year reign atop the fledgling league, tonight's victory more than restored any prestige it may have lost. In August, D.C. earned a spot in the InterAmerican Cup by defeating two strong Mexican teams to gain a surprise triumph in the North/Central American and Caribbean (CONCACAF) championship.

Vasco had been away from home for three weeks to play United and Real Madrid, so it probably wasn't enthused about being here tonight. However, it put everything into the match. For motivation, all its players needed was to hear the reports from Rio de Janeiro, where rival club Flamengo was celebrating Vasco's loss to Real Madrid.

Flamengo supporters took to the streets, setting off fireworks and blowing their car horns. The next day, quarter-page ads appeared in newspapers sarcastically congratulating Vasco for being "world vice-champions." The ads were signed by Flamengo's "world champions" -- a title it won 17 years ago.

Except for one defender, Vasco's starting lineup tonight was the same one it used for the game against Real Madrid. But as in the opener of this series, United created more scoring opportunities than Vasco did. And this time it was rewarded.

Late in the first half, some fine one-touch passing between Jaime Moreno and Etcheverry freed Jeff Agoos, who was charging forward from his left back position. Agoos drilled a low pass through the penalty area that Lassiter allowed to skip toward the far post, where Sanneh finished with a sliding touch past goalkeeper Carlos Germano.

Shaken by the goal, Vasco turned to trickery to create a chance three minutes later as Donizete took an obvious dive several seconds after United midfielder John Harkes made minor contact. A foul was called, but instead of berating the referee, Harkes shouted at Donizete for his theatrics. Vasco's ensuing free kick ended in a stray shot from 20 yards.

In the second half, D.C.'s defense began to bend. Donizete had two ideal opportunities in the 56th minute, but he hit the crossbar and goalie Scott Garlick blocked a rising shot. After Pope's goal, Garlick made two more excellent saves to prevent the overtime.

"Hopefully, this will show a few people around the world that we have some good teams in our league," said Pope, who won the CONCACAF championship with the only goal against Toluca of Mexico and the 1996 MLS final with a sudden-death overtime score. "We played with a lot of emotion and definitely thought we could do it. It's an amazing thing. We actually did it, we really did it." United Notes: United finally completed the trade of Argentine defender Mario Gori to Miami for the Fusion's first-round pick in the 2000 college draft. The teams also swapped second-round picks in the 1999 draft, with United moving from 19th overall to 17th. D.C. also has the first overall pick, acquired from New England. CAPTION: Marco Etcheverry watches teammate Ben Olsen battle Nasa. Tony Sanneh and Eddie Pope scored for D.C. United. ec