Sir Alex Ferguson watched Arsenal blow the Premier League title race wide open with a 1-0 victory against his Manchester United team at the Emirates Stadium and cited a refereeing injustice among his post-match regrets, going so far as to claim that "we're not going to get the decisions in these big games, I'm afraid".

The United manager was astonished not to be awarded an 88th-minute penalty for what looked to be a foul by Gaël Clichy on the substitute Michael Owen. Arsenal had earlier been denied a penalty of their own for a handball by the United captain, Nemanja Vidic, which even Ferguson admitted should have been given, yet he has long been unconcerned about accusations of him being one-eyed.

In his criticisms of the officials Ferguson has increased the pressure on the team that will take charge of Chelsea's visit to Old Trafford on Sunday, in what looks increasingly like a title decider. Chelsea beat Tottenham Hotspur 2-1 at home on Saturday, with the help of two fortunate decisions, to close to within three points of United.

Ferguson was furious with the officiating in his team's 2-1 league defeat at Chelsea on 1 March and was unhappy with key decisions in both the league fixtures between the teams last season, which Chelsea won, notably when Didier Drogba was in an offside position when he scored what proved the decisive goal at Old Trafford. Chelsea might point out that they were wronged in the Champions League quarter-final first leg at Stamford Bridge, when Ramires was denied a late penalty.

"It gives Chelsea a major chance now," Ferguson said, after Aaron Ramsey's 56th‑minute goal condemned United to defeat here. "They got great decisions for them [on Saturday] and they seem to get these decisions at the moment.

"They got one to win the league last season at Old Trafford. So that's a worry. You go into a game worrying about these things. But in terms of ability, a game at Old Trafford ... the league at stake ... our supporters will be ready for it and so will my players."

Ferguson has only just returned to the dug‑out after serving a five-match touchline ban for his comments about the referee Martin Atkinson after the Stamford Bridge league game and his latest remarks are sure to go down badly at the Football Association.

Arsène Wenger, the Arsenal manager, conceded that "you can give a penalty" for Clichy's challenge on Owen. "It must have been a penalty," Ferguson said, ruefully. "I think the first one was definitely a flick of the hand from Vida but it was very difficult to see that one. I never saw it and nor did the linesman or the referee. But I think we all got a clear view of the second one – it was a clear penalty kick. We are not going to get decisions like that in a major game. It's too big a game and we don't seem to get these decisions."

Robin van Persie, who might have converted Theo Walcott's 33rd‑minute cross but for Vidic flicking the ball away with his hand, said the incident represented "a clear penalty and, in my opinion, a straight red card".

"It balances out in that respect," Ferguson said. "It was a flick of the hand from Vida but it was difficult to see that. Van Persie was the only one who saw that; he was the only one who complained. The one at the end Clichy immediately knew. He threw his hands up in horror. Owen was definitely brought down."

Owen said, in a tweet: "Not seen tv replay but don't need to as I know mine was a pen. Heard people saying Arsenal should of had one too so can't complain too much. That was a kick in the teeth. We were not happy with our performance but it is important to put today behind us now and focus on things we can affect in the future. Still in a great position so time for one final push."

Ferguson was disappointed that his team had started to play only after they had fallen behind to Ramsey's goal buthe sounded a note of optimism and defiance. United entertain Schalke on Wednesday in the Champions League semi-final second leg, 2-0 in front from the first leg.

"We're in as good a position as you could ever wish for at the start of the season – semi-final of the European Cup, second leg, two-goal lead and we go into [Sunday's] game equal goal difference and it's a home game," he said. "I'll make some changes on Wednesday without question ... bring Scholes back in, Berbatov, Michael Owen, fresh players ... also probably keep my experienced players at the back.

"We deserved a point here. Bear in mind, I don't think Edwin van der Sar had to make a save. Arsenal play a lot of nice football but they never looked like scoring. They got a goal from their only shot on target so it was a bit disappointing."

Wenger lamented how his team could beat United yet drop points against lesser opposition at home. "It makes it more frustrating," he said. "But I prefer to be more frustrated than to lose the game today.

"We had a good performance with everything in it – discipline, fighting spirit and our usual passing game. The team maybe lacks a bit of maturity under pressure and it has also had to deal with some big disappointments. We were really unlucky this season until now. Let's hope we have a bit more luck in the final three weeks. I am very happy for Ramsey. When you think that his injury happened 14 months ago. Now he looks back to his best."