Jurgen Klopp conceded his Liverpool side were nowhere near their best in the 2-1 defeat to Manchester United.
The Reds started the match as favourites but were blown away by the home team's aggression and tenacity as goals from Jadon Sancho and Marcus Rashford cancelled out Mohamed Salah's consolation.
The result leaves Liverpool down in 16th without a win, already seven points behind early pacesetters Arsenal.
Klopp told BBC Sport: "The start of the game was exactly what everyone excepted, what United fans expected, they were after us. They started slightly more aggressive than us, they could more play the game they wanted than we could play the game we wanted.
"They scored the goal, which we had to defend differently, but that is how it is with goals. In the second part of the first half we were there and caused them problems. We had massive chances.
"At half time we showed the boys a couple of situations we did really well and wanted to do that again but then we conceded the second goal. Then we have to chase the game properly and then you can get in a bit of a rush.
"We scored a goal and we deserved in that period and then you have to force it, we tried, have to admit in the end not good enough and that is why we lost.
"I don't have a lot of arguments, we lost the game. On another day, with more conviction about what we are doing, we can turn it around. That is how it is.
"To play the football we are able to play, we want to fight. We have a good home game on Saturday and Anfield has to be rocking. We have to set the fire and the rhythm.
"We will try absolutely everything that every Liverpool supporter will expect - we will fight for our lives."
That game on Saturday is against Bournemouth, who most recently lost to Arsenal but have picked up a win courtesy of their opening day success against Aston Villa.