Sky Sports pundit Gary Neville, co-commentator at Anfield, said that Steven Gerrard had been brought on to help Liverpool, but his "stupidity" costs his side the match.
Gerrard was brought on in place of Adam Lallana at half-time but lasted less than a minute on the pitch before seeing red for his stamp on United's Ander Herrera.
"He's on for more reasons than one," Neville said on Sky Sports.
"His one (tackle) on Mata was a crunching challenge but I think he might have been stupid. Steven Gerrard will know from the experience that he has.
"It's the emotions sometimes - when you're playing a fixture like this."
Liverpool lost the all-important clash with their rivals 2-1 to fall five points behind United who occupy fourth spot.
