Sir Alex Ferguson blamed Chris Foy for Manchester United's damaging 1-0 defeat against Arsenal after the referee refused to give his side a late penalty at the Emirates Stadium on Sunday.
Ferguson's side were pushing for an equaliser in the closing stages when Arsenal defender Gael Clichy caught substitute Michael Owen with his trailing leg.
It looked like a penalty but Foy rejected United's appeals and Arsenal held on for a win that left the leaders only three points ahead of second placed Chelsea, who travel to Old Trafford for a massive showdown next Sunday.
Ferguson admitted United could have conceded a penalty themselves when Nemanja Vidic handled Theo Walcott's cross in the first half, but Ferguson believes Foy's refusal to penalise Clichy has potentially transformed the title race.
"It's too big a game not to get the decisions right," Ferguson told Sky Sports.
"It balances out in that respect but I think it was difficult to see that one (Vidic's handball) but the one at the end, Clichy knew, he put his hands up in horror."
"Obviously, it gives Chelsea a major chance now and that's what happens when you get these decisions."
"They got one at Old Trafford last season (when Didier Drogba scored despite being offside) so that's the worry now."
Ferguson felt his side deserved at least a draw from the match even though they were well below their best before and after Aaron Ramsey's 56th-minute winner.
"After the goal we dominated and I think we deserved something," he said.
"I think we didn't use the ball properly but once we lost the goal we were in their half most of the time."
After looking odds-on to win a record 19th league title, United will now surrender first place to Chelsea on goal difference if the reigning champions win at Old Trafford next weekend.
However, Ferguson expects a rousing display against Chelsea in a game that would still virtually seal the title for United if they win.
"In terms of ability - a game at Old Trafford, the supporters will be ready for it - and so will our players," he added.
While Arsenal retain faint title hopes, this victory was more important for the belief it should give them next season after a miserable run over the last two months.
Dutch striker Robin van Persie provided the assist for Ramsey's winner and he claimed his side "wanted it more".
Van Persie felt Arsenal should have had a penalty for the Vidic incident and he told Sky Sports: "It was a clear penalty and in my opinion a straight red.
"If United should have had a penalty then it's 1-1 on that one but in the end I think we played better today."
"We wanted it more. They played just on the counter-attack so in the end I think a fair result."
"It was all about pride today. The fans were great. It was up to us to show some dignity and some honour. We did that today so we're very pleased with that."