Liverpool's hopes of winning the Europa League were left hanging by a thread after they lost 3-0 at home to Atalanta in the first leg of their quarter-final tie on Thursday, while Bayer Leverkusen beat West Ham United to extend their unbeaten record this season.
Liverpool, who started with Mohamed Salah and Dominik Szoboszlai among the substitutes, saw Harvey Elliott come agonisingly close to opening the scoring with a shot that hit the bar and struck the post on its way back out.
Atalanta then took the lead seven minutes before half-time when Davide Zappacosta's low ball in from the right was finished off first-time by former West Ham striker Gianluca Scamacca.
The same player made it 2-0 on the hour with a fine finish from Charles De Ketelaere's assist.
Salah, who had come on at the start of the second half, then had a goal disallowed for offside before Atalanta made it 3-0 with seven minutes left.
Recent history suggests there is still hope for Klopp's side, as they won 5-0 away to Atalanta in Bergamo in the Champions League group stage in 2020/21, a campaign in which they also lost to the Italian side at Anfield.
In Germany, Bundesliga champions-elect Leverkusen made it 42 games without losing in any competition this season as they beat West Ham 2-0 to seize control of their quarter-final tie.
Jonas Hofmann and Victor Boniface both came off the bench to score late goals for Xabi Alonso's side, with the opener arriving in the 83rd minute and the second coming in injury time.
The victory continues what could be a stunning week for Leverkusen, who are 16 points clear of Bayern Munich in Germany and can win their first Bundesliga title by beating Werder Bremen at home on Sunday.
If Leverkusen finish the job against West Ham, they will advance to a semi-final against either AC Milan or Roma, who clashed at San Siro in the first leg of their quarter-final on Thursday.
Roma ran out 1-0 winners on the night away to their Serie A rivals thanks to Gianluca Mancini's 17th-minute header from a corner. Mancini had also scored the winner in the Rome derby against Lazio last weekend.
Thursday's other game saw Benfica beat Marseille 2-1 in Lisbon in the first leg of their quarter-final. (AFP)