Cruz Azul piled up a 16-7 edge in shots against a D.C. team fielding only three regular starters: Jaime Moreno, Marc Burch and Devon McTavish. Santino Quaranta, substituted early in last Sunday's 3-0 loss to Dallas, didn't get off the bench.
The visitor left Carlos Bonet and Mexican international Gerrado Torrado in Mexico City and Paraguayan veteran Cristian Riveros started the match on the bench.
United's attack tested Cruz Azul several times but its failure to take the lead enabled the Mexicans to gain the upper hand after a tepid beginning. D.C. didn't play brilliant soccer yet it showed much more heart than it had succumbing to FC Dallas last weekend.
Five minutes into his first-team debut for D.C., on-loan defender Greg Janicki got on the end of Moreno corner kick and headed it wide. A few minutes later Moreno tried to chip Cruz Azul keeper Alfonso Blanco but his effort floated just over the bar, and midway through the half Moreno played a through ball that Quevas Kirk couldn't steer past Blanco. Francis Doe tucked away a Kirk cross in the 26th minute but an offside flag nullified the goal.
Zeballos entered the match in the 30th minute as an injury substitution for Marcelo Carrusca, who left the field on a stretcher after a heavy collision. Cruz Azul nearly took the lead late in the half but Rod Dyachenko tracked back to clear a Cesar Villaluz lob from under the crossbar.
Eleven minutes into the second half, Burch blocked a shot and the ball rebounded out to Villaluz, who struck a low shot from the right side that was headed well wide of the net, but it struck Zeballos as he tried to get out of the way. Wells, completely wrong-footed, had no chance to recover and the ball cleared him by a wide margin en route to the net.
Thabiso "Boyzz" Khumlo's entry in the 61st minute sparked the D.C. attack, but still United failed to score. Khumalo hit the post from a sharp angle, and Cruz Azul also struck the woodwork with Wells straining to reach the ball. A careless Burch giveaway presented Zeballos with a chance that Burch recovered in time to block.
D.C. will resume league play Saturday at RFK against Chivas USA without Moreno, who will serve a two-game suspension for striking FC Dallas midfielder Andre Rocha in the 3-0 loss on Sunday.
Midfielder Marcelo Gallardo, out for nearly a month with an adductor injury, has trained this week and may be available for United, which returns to CCL play Oct. 9 against Deportivo Saprissa in San Jose, Costa Rica.
Saprissa (Borges 68, Alpizar 86) 2 Marathon (Nunez, pen., 50) 1
D.C. United 0 Cruz Azul (Mexico) 1
STANDINGS: Marathon (6 points) Cruz Azul (6), Saprissa (6), D.C. United (0).