Liverpool manager Juergen Klopp said it was baffling that the Premier League champions were not awarded a penalty in Monday's 1-0 loss at Southampton and claimed other teams would not have been denied by the officials.
Liverpool fell behind to a second-minute lob by former striker Danny Ings and had a penalty claim dismissed when Georginio Wijnaldum's shot from inside the box was blocked by the hand of Jack Stephens.
The league leaders were left frustrated again when Kyle Walker-Peters went unpunished after bringing down Sadio Mane in the penalty area.
"The best situations we had were with Sadio having the ball at his feet," Klopp told Sky Sports. "For anyone to say he's a diver is the biggest joke...He had two situations where other teams would get a penalty.
"The handball, I don't know who will explain that to me. In these situations we were unfortunate...I hear Manchester United had more penalties in two years than I had in 5-1/2 years. I have no idea if that's my fault, or how that can happen.
"But it's no excuse for the performance. We cannot change it, we have to respect the decisions. We can change our performance. That's our focus now."
Former Liverpool defender Jamie Carragher said the club had forgotten how to play in the final minutes of games after going three league matches without a win.
"I didn't see that coming, I expected a reaction on the back of two poor performances. We've just seen another one," Carragher told Sky Sports.
"Liverpool's away form this season is so poor...That's a big worry, in terms of what they're creating away from home. It's nowhere near enough."
Liverpool face Aston Villa in the FA Cup third round on Friday before a league clash against United on Jan. 17.