Oguchi Onyewu, who earlier this month became the first American-born player to sign a contract with AC Milan, made his debut to begin the second half Wednesday.
Just one day after practicing for the first time with his new teammates, Onyewu had been on the field only 10 minutes when Salvador Cabanas' pass looped over his head and Enrique Esqueda used a high kick to beat goalkeeper Marco Storari's late dive to the left.
AC Milan's Filippo Inzaghi scored on a breakaway 66 minutes into the exhibition match.
He ran past Club America defenders Guillermo Cerda and Ademar Rodriguez to beat goalkeeper Armando Navarrete's late dive to the left.
Marquez made it 2-1 in the 84th minute.
Many of the 53,600 fans at the Georgia Dome cheered Onyewu in his debut with AC Milan.
After getting a welcome hug from midfielder Clarence Seedorf, Onyewu was announced to replace defender Alessandro Nesta.
Club America beat Inter Milan 5-4 on penalty kicks Sunday in Stanford, Calif.
Ronaldinho, Seedorf and Gianmarco Zigoni each had three shots for AC Milan.