Dominik Szoboszlai produced a sublime goal and a ridiculous error as Liverpool eased to a 4-1 win over third-tier Barnsley to reach the FA Cup fourth round.
The Hungarian international unleashed a rocket into the top corner from long range to open the scoring at Anfield on Monday before Jeremie Frimpong doubled the home side's lead.
But Szoboszlai gifted the League One side a route back into the tie when he fluffed an attempted backheel inside his own box and Adam Phillips gratefully smashed home.
Barnsley boss Conor Hourihane claimed Szoboszlai's lax move was disrespectful and not one he would have tried in a Premier League game, said AFP.
Arne Slot was also far from happy with his midfielder, who has been Liverpool's outstanding performer so far in a difficult season for the English champions.
"I don't think you should do that in a FA Cup game, or a League Cup game, or in a friendly game, or in a training session. It was a weird choice," said Slot.
"I also have my opinion about it but I prefer to keep that to myself and speak about that with Dom."
Hourihane was furious his side were not awarded a penalty midway through the second half for a trip by Szoboszlai on Reyes Cleary.
Slot was forced to empty his bench of key players as Florian Wirtz, Hugo Ekitike, Ibrahima Konate and Ryan Gravenberch were introduced just after the hour mark.
Liverpool labored going forward for most of the second period until their star duo of attacking substitutes clicked to clinch victory in the final six minutes plus added time.
Ekitike's deft flick found Wirtz, who curled into the top corner for his third goal in five games since breaking his duck in his 23rd appearance for the Reds.
The roles were reversed in stoppage time as Wirtz unselfishly crossed for Ekitike to tap in.
"We scored nice goals but I think for too long the game was tight," added Slot.
"Two-nil up then giving a goal away like that made it difficult until 10 minutes before the end."
Liverpool's reward is a home tie against Manchester United's conquerors Brighton in round four.
