Moreno entered at halftime and Emilio - the league's leading scorer with 20 goals -- played the final 12 minutes of a game riddled by 42 fouls. Chicago committed five more than D.C. United, which responded to the Cuauhtemoc Blanco threat with persistant fouling.
In the 14th minute, Chicago defender Gonzalo Segares lobbed a long ball into D.C. United territory that D.C. defender Greg Vanney headed into Rolfe's path. Rolfe hammered an unstoppable high shot past keeper Troy Perkins.
Four minutes later, Blanco forced a diving save from Perkins, who had four saves on the day.
Rookie Guy-Roland Kpene, who has yet to score an MLS goal, spearheaded the D.C. offense until being replaced by Moreno in the second half, when D.C. threatened more frequently, mainly through Christian Gomez.
The Chicago victory extended its unbeaten postseason streak against D.C. United to six games, with five wins and one tie. D.C. United has not scored in those six games.
"They took care of their home field and now we have the chance to take care of ours," midfielder Ben Olsen told the Washington Post . "Would I have liked a tie or win? Absolutely. But the situation is not panic time and we have to go ahead and take care of our home."
Emilio believes he'll be back to 100 percent fitness for the second leg next Thursday at RFK Stadium. The series will be decided on total goals.
Oct. 25 in Bridgeview, Ill. Chicago 1 D.C. United 0. Goal: Rolfe 14. Chicago - Pickens, Robinson, Brown, Conde, Segares, Pause, Rolfe, Armas, Gutierrez, Barrett (Carr, 63), Blanco (Thorrington, 85). D.C. United - Perkins, Namoff, McTavish, Vanney, Burch, Olsen, Carroll (Emilio, 78), Simms, Fred, Kpene (Moreno, 46), Gomez. Yellow Cards: Chicago - Gutierrez 12, Brown 51; D.C. United - Carroll 22, Moreno 86. Referee: Baldomero Toledo. Att.: 17,834.