The Eastern Conference-leading Crew (11-4-4) had been 0-2-2 away from home since a 1-0 victory at Kansas City on May 23.
Sebastien Le Toux scored for the Union (4-9-3), who dropped to 3-2-2 at home.
Lenhart's tiebreaking goal was the result of a dazzling play. Emilio Renteria crossed the ball in front of the net and Lenhart sprawled out for a diving header past Philadelphia goalkeeper Chris Seitz.
Columbus went ahead 1-0 in the 43rd minute when Guillermo Barros Schelotto sent a free kick from about 35 yards out toward the far post. Lenhart, who entered the game in the 27th minute for Jason Garey, got behind the Philadelphia defenders and knocked a header into the net.
The Union tied the score when Le Toux was awarded a penalty kick and proceeded to score his team-best ninth goal in the 3rd minute of first-half stoppage time. Columbus Frankie Hejduk was whistled for a yellow card for tripping up Le Toux in the penalty box just before the half expired.
(Copyright 2010 Philadelphia Union. Reprinted by permission)