Liverpool slumped to a shock 3-0 home defeat by Atalanta on Thursday as Gianluca Scamacca struck twice for the Italian side in their Europa League quarter-final first leg.
On a chastening evening for former European champions in the continent's second-tier club competition, AC Milan lost 1-0 at home to fellow Italian side AS Roma.
Atalanta took the lead at Liverpool after 38 minutes when an unmarked Scamacca struck a low shot past keeper Caoimhin Kelleher from Davide Zappacosta's pinpoint pass.
Scamaca pounced on poor Liverpool defending to fire home from a fine cross by Charles De Ketelaere in the 60th minute before Mario Pasalic sealed the rout seven minutes from time.
Late strikes by Bayer Leverkusen substitutes Jonas Hofmann and Victor Boniface earned the Bundesliga leaders a 2-0 home win over West Ham United.
The visitors' keeper Lukasz Fabianski pulled off a string of saves to keep the scores level at the break before Hofmann gave Leverkusen the lead in the 83rd minute and Boniface doubled the advantage in stoppage time with a header.
Roma upset hosts AC Milan thanks to Gianluca Mancini's pinpoint header from Paulo Dybala's corner in the 17th minute.
Portuguese champions Benfica claimed a 2-1 home win over Olympique de Marseille through goals by Rafa Silva and Argentine forward Angel Di Maria.
The second legs will be played next Thursday.
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