Five-times European champions Liverpool slumped to a 2-1 defeat against Besiktas on Wednesday and now face an uphill task to progress from Champions League Group A.
Last season's finalists have just one point from their first three games and are bottom of the group. Besiktas have three points, Porto are on five and Olympique Marseille lead the way with seven.
"The first thing is start to think about the next game, try to win that one," said Liverpool manager Rafa Benitez. "I think Liverpool can qualify with seven points."
England midfielder Steven Gerrard said the club had "a mountain to climb".
"The worst possible result we could have hoped for," he said. "We had a mountain to climb before this game, we have an even bigger one now."
Besiktas took the lead in the 13th minute with a Sami Hyypia own goal after a close-range Serdar Ozkan shot deflected in off the Liverpool defender.
Brazilian striker Bobo doubled the lead after 82 minutes, firing a shot in through the legs of Liverpool goalkeeper Pepe Reina.
Gerrard pulled a goal back with a diving header with five minutes remaining but it was not enough to save Liverpool.
The visitors, already under intense pressure with only one point from their opening two fixtures, were further unsettled by the opening goal after a clearance rebounded off Steve Finnan into the path of Serdar.
Liverpool looked to hit back with efforts from John Arne Riise, Andriy Voronin and Gerrard, who was put through on goal but was denied by Besiktas keeper Hakan Arikan.
But the English side were constantly under threat from swift counter-attacks from Besiktas, boosted by a weekend league victory against Trabzonspor.
The home side came under pressure in the second half with Gerrard firing just wide and Hakan also saved from Ryan Babel, but Bobo's goal left Liverpool with too much to do.
"We could win the group. There are nine points remaining and we will try and win all of them," said Besiktas coach Ertugrul Saglam, who was forced to watch the match from the stands after being sanctioned by UEFA over an incident in the club's previous Champions League fixture.