Union substitute Anthony Ujah scored in the 86th minute to set up an exciting finale but Frankfurt weathered the home side's late push. "A point would have been deserved, but in the end Frankfurt were more efficient than we were," Union coach Urs Fischer said.
Fischer's side made a great start and almost took an early lead when goalkeeper Kevin Trapp just denied Marvin Friedrich after a corner. Silva had Frankfurt's first chance 10 minutes later when he was through on Rafal Gikiewicz's goal, but Friedrich got back to put him off and Gikiewicz gratefully snapped up the ball.
Robert Andrich went close for Union in the 29th before Frankfurt gradually gained more of the ball with good chances falling to Dost, Silva and then Filip Kostic before the break. Dost, making his first Bundesliga start for Frankfurt, finally scored in the 48th by prodding home from close range after Gikiewicz could only parry Kostic's effort.
Many of the traveling fans may have missed the goal due to more pyrotechnics in the away end at the beginning of the second half. The game had started under a cloud of smoke from their first exhibition.
Union was unable to replicate its early intensity and Silva ended its hopes of even a point when he scored with a header to Djibril Sow's cross in the 62nd. It leaves Union one point above the relegation zone ahead of the rest of the sixth round, while Frankfurt is up to sixth.
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Ciarán Fahey on Twitter: https://twitter.com/cfaheyAP