But after a tough first half, Klopp’s side improved in the second, and flooding into the final third looked to have been denied a number of penalty shouts by Marriner.
Firstly, Gini Wijnaldum‘s shot was blocked by the trailing arm of Jack Stephens, before Mane appeared to have been fouled in the box on a number of occasions, most notably under pressure from Kyle Walker-Peters.
In his post-match press conference, Klopp highlighted the penalty decisions as questionable, calling Marriner to task as he detailed a number of incidents.
“I turned around in the situation, we had a really good view of it and it looked like a clear penalty, I turned around to the fourth official and he said ‘we checked already, no penalty’,” he said.
“That’s the 100 percent truth, and now if somebody wants to tell me how quick they had it in all these different angles, but that’s 100 percent, ‘we checked it already, no pen’.
“There were moments last year, I think the penalty against Leicester, and people said ‘Sadio Mane, going down that easily’.
“If this boy went down easily, we would have had a penalty this time and last game a stonewall penalty.
“But what Andre Marriner did with Sadio Mane tonight, I’m not sure that’s OK, to be honest.
“The boy tried absolutely everything, there were a few great challenges, but there were a lot of situations which should have been free-kicks as well.
“The last situation when he goes down, you see that in the box, he hits him in the end with his left foot and that’s another penalty.
“We cannot change it. I heard now that Man United had more penalties in two years than I’ve had in five-and-a-half years; I have no idea if it’s my fault, I don’t know how that can happen.”
However, while his criticism was warranted, Klopp was quick to stress that this was “no excuse” for his side’s poor performance.
“But that’s no excuse for the performance of tonight, because that’s something we can change,” he continued.
“The rest we cannot change, we have to respect the decision. Our performance we can change, and that’s where we will put all our effort in now.”
Liverpool are next in action on Friday night, and a trip to Aston Villa in the FA Cup, for which Klopp will demand a strong performance from a side likely much-changed from the St Mary’s defeat.