Weah, the son of Liberia President and former FIFA Player of the Year George Weah, ran onto a pass from Mendez at the top of the penalty area, used his right foot to poke the ball through the legs of Qatar captain Ahmed Suhail, then beat goalkeeper Shehab Mamdouh with a right-footed shot from 14 yards.
Brandon Servania was pulled down by Ahmed Alminhali in the 80th minute, but Mandouh dived to his right and batted away Mendez's penalty kick. Richard Ledezma hit the crossbar from 18 yards in the seventh minute of stoppage time.
Ukraine won the group with two wins and a draw after tying Nigeria 1-1 Thursday and will play a third-place team in the round of 16. Nigeria is assured of advancing as a third-place team. U.S coach Tab Ramos made three changes, inserting goalkeeper David Ochoa, Mark McKenzie and Servania for goalkeeper Brady Scott, Sergiño Dest and Paxton Pomkal.
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