Juergen Klopp said his Liverpool side were mentally not fresh after a damaging 1-0 home defeat by Brighton & Hove Albion on Wednesday left them way adrift in the Premier League title race.
Liverpool appeared to have rediscovered their spark with consecutive away wins last week over Tottenham Hotspur and West Ham United but were easily stifled by an impressive Brighton side.
Klopp's champions failed to score for the third successive home league game and they managed only one effort on target as they fell seven points behind leaders Manchester City who also have a game in hand.
"We played against really good opposition, that's clear," Klopp said. "We looked mentally not fresh. They deserved to win.
"We wanted to play better and more convincing. We lost too many balls in promising situations. I know the boys can play pass A to B but today B did not seem reachable.
"We had a really tough week. We were not fresh tonight and that's when you have to find a way."
Finding a way is what Liverpool have made a habit of over the last two seasons but suddenly, at Anfield at least, they have run out ideas. Premier League leading scorer Mohamed Salah barely had a sight of goal and when he did have a chance in the first half he blazed it over the bar.
Striker Sadio Mane's absence because of injury did not help Liverpool's cause while at the back they looked vulnerable against the clever approach play of Brighton who claimed a first league win for the south coast club at Anfield since 1982.
Considering Klopp's lack of options because of injuries to defenders Virgil van Dijk, Joe Gomez and Joel Matip that is perhaps understandable, although new defensive signing Ben Davies was left as an unused substitute.
"The only explanation now is that we are a fatigued team, mentally more or less," Klopp said.
"We had our moments but they deserved to win. We had to defend with a lot of running, there is no formation in the world where you are always in the right place.
"The best way to defend against a team like that is to keep the ball yourself but we couldn't do it tonight. It has been a tough week and tonight it was not enough."
Liverpool's next league game is at home to Manchester City on Sunday.
"City are flying and we have to find solutions," Klopp said.
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