Alan Pardew was upset that Marcos Rojo was not sent off as Crystal Palace slipped to a contentious 2-1 home defeat against Manchester United.
Zlatan Ibrahimovic scored United's late winner at Selhurst Park after James McArthur cancelled out Paul Pogba's first-half opener.
Pogba's close-range finish was doubly controversial as the France international was in an offside position and the ball appeared to be handled by Ibrahimovic following Juan Mata's free kick into the box.
Referee Craig Pawson allowed the effort to stand, and Rojo remained on the pitch after a two-footed lunge on Wilfried Zaha in the 38th minute, which saw the Argentinian defender shown a yellow card.
The hosts benefited from two strokes of luck in the second period when substitute Joe Ledley escaped punishment after handling in his own box before Mata had a goal wrongly ruled out for offside.
Eagles manager Pardew told BT Sport 1: "Rojo's tackle is dangerous, it's another two-footed tackle, I think he did one before [against Everton]. He was a bit fortunate to get away with that.
"We can't really lean on that though because the players have given everything tonight. We were a little bit short of bodies and we've got a big game Saturday [at Chelsea] so we've got to take what we can out of this game in terms of our confidence levels.
"It's just so galling for us to get that blow at the end because it was real quality what Pogba did [in assisting the winner], the weight of the pass and the finish. It was a shame because a point would have been important for us tonight. The shape of the team and the effort they put in deserved reward really.
"We worked hard on making sure it was very, very difficult for United to play through us, which we did well. We could've done better on the break but I can't fault them, they've given me everything and we need a little break here and there and we'll be okay.''
Of the Rojo decision, Pardew's opposite number Jose Mourinho said: "[Pawson] is good. He is one of the good, young referees.
"If he made mistakes then that is unfortunate but we need to support young referees.''
Still, Pardew was disappointed his side did not get anything out of the game, as the result sees them slip to 16th in the league, but he admits there were a number of errors in defence as well as some less-than-stellar play from Christian Benteke.
The Eagles boss said: "Defensively I thought we could have done a little better in the first half.
"Second half we had a good spell, got a great goal and it was a shame that we couldn't kick on. In the end we were undone by two great players.
"I think Christian [Benteke] had a quiet night tonight, our hold-up play could have been better. We had a bit more aggression. I feel for them because they deserve a break.''