Jurgen Klopp bemoaned his "surprised" Liverpool players who he claims should've been ready from the start.
The Reds lost for the second time this season as they were undone by Southampton which saw them give up more ground in the title race.
Danny Ings' winner came after 111 seconds as his smart finish left Alisson with no chance.
Liverpool were far from their best in the first-half and took 75 minutes to register a shot on target.
It is the second time they've failed to score in the space of five days following their goalless draw at Newcastle.
Klopp clearly had issues with several elements of his side's performance but particularly lamented their slow start.
He told BBC Sport: "What was disappointing? How long have we got – the start obviously. Not only the goal but the start in general. Congratulations to Southampton they deserved it.
"You know exactly what you are going to get from them, you cannot be surprised but we looked surprised.
"At the beginning how we played, where we lost the balls, it's not rocket science. We should have done much better. We played into their hands with the start.
"They put a lot of work in. Our decision making was just not good. That is how it is when you don't have momentum. We should have had much more chances.
"These are outstanding players but they were not ready from the start. Sadio Mane should have had a penalty tonight, and there was the handball – I've no idea.
"It's not an excuse for the performance but you can get a point if they are given. Now we have to show a reaction."
Liverpool can now be overtaken in the league by both Manchester clubs.
They take on Manchester United at Anfield next summer but Manchester City, provided they win their games in hand, can go two points clear of the Reds.
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