Liverpool endured a humbling night after Atalanta left Anfield with a 3-0 victory that places the Serie A side on the brink of qualifying for the Europa League semi-finals.
Former West Ham striker Gianluca Scamacca struck in each half, the second goal made possible by a superb pass from Charles De Ketelaere, before Mario Pasalic added the third in the 84th minute.
Jurgen Klopp’s Premier League title challengers were completely outplayed by opponents positioned sixth in their domestic league and as a result have a mountain to climb in the second leg of their last eight tie.
West Ham were breached by two late goals as they slipped to a 2-0 defeat in their first leg at Bayer Leverkusen.
The Hammers had defended heroically for 83 minutes before goalkeeper Lukasz Fabianski was finally beaten by substitute Jonas Hoffman.
The second arrived in stoppage time when a second sub, Victor Boniface, headed home Hofmann’s cross to leave West Ham’s hopes of a third consecutive European semi-final looking slim.
Benfica took a step towards the reaching the last four after dispatching Marseille 2-1 in Lisbon through goals by Rafa Silva and Angel Di Maria.
The Portuguese champions were on target either side of the interval with David Neres involved in both strikes before Pierre-Emerick Aubameyang netted what could be an important away goal with 23 minutes remaining.
Gianluca Mancini’s early goal was all that separated AC Milan and Roma in their all-Serie A tie at the San Siro.
Milan controlled most of the game but did not recover from Mancini’s effort with Olivier Giroud directing a short-range target on to the crossbar in the closing moments.
Aston Villa clawed a slender advantage from their Europa Conference League quarter-final against Lille after emerging with a 2-1 first-leg win at Villa Park.
Goals in either half from Ollie Watkins and John McGinn saw Villa lead their first European last-eight tie since 1998 and give boss Unai Emery victory in his 1,000th match as a manager.
Bafode Diakite’s late header gave the French side a lifeline just as it looked like they would head home frustrated by Villa goalkeeper Emiliano Martinez, who had made a string of big saves.