Liverpool have 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 on Thursday night (Friday AEST), before Mario Pasalic added the third in the 84th minute.
Jurgen Klopp’s Premier League title challengers were completely outplayed by a side sixth in their domestic Italian league.
Klopp called the loss a “low point” in Liverpool’s season.
Liverpool looked flat throughout and ended the night perhaps fortunate Atalanta had not taken one of the many late chances they had.
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Harvey Elliott hit the post in the first half and Mo Salah had a goal ruled out for offside in the second, but Liverpool lacked the spark needed to beat a well-organised Atalanta side, who will be confident of finishing the job next Thursday in Bergamo.
But first Klopp must lift his players for Sunday’s visit of Crystal Palace in the tight battle at the top of the Premier League table.
“It was a really bad game, oh my God,” Klopp said after Liverpool’s first home defeat in nearly 14 months.
“We started well, really well, and then didn’t continue. They broke, they scored and we just lost the plot a little bit.
“We played a bad game and we deserved to lose. We must feel that now, but we have exactly this night to feel bad about it and then we have to build up for Palace.”
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 goal 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 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.
Meanwhile, 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 1000th 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.
Elsewhere, Olympiacos overcame a late comeback from Fenerbahce to win 3-2, Club Brugge beat the other Greek side PAOK 1-0, and Fiorentina drew 0-0 at Victoria Plzen.