While the ten-man Hammers were being forced to get gritty against Lyon in East London, Eintracht Frankfurt were giving Barca an awkward evening in Germany.
In just their second home game since Bundesliga sides have been allowed capacity crowds again, more than 50,000 supporters created an incredible atmosphere inside Deutsche Bank Park.
Eintracht looked to raise the decibel levels even further as they tried to get at Barca early on.
But they could have fallen behind within three minutes, only for Kevin Trapp to tip a brilliant, rising Ferran Torres effort from range over the bar.