Sir Alex Ferguson sounded a warning to Chelsea after his Manchester United side closed the gap on the Premiership leaders to seven points.
Ferguson's side are in hot pursuit of league leaders Chelsea
Chelsea have taken four points from their last three matches, while United have won their last eight league games.
"This has asked a question of Chelsea," said Ferguson.
"I always think the important thing is if your form is good in April you have got a chance, if your form is stuttering you can throw it away."
Ferguson's side play rivals Arsenal next Sunday and he now believes that game will have a major say in whether United can overtake Chelsea in the last six games of the season.
Chelsea were held to a 0-0 draw by Birmingham on Saturday, while Ferguson's team beat Bolton 2-1.
And the Old Trafford boss has been quick to seize on the slip-up by the Blues to pile on the pressure for the Stamford Bridge outfit.
"Everyone expected them to beat Birmingham and they didn't," said Ferguson, whose side face Chelsea away in the penultimate game of the season.
"They still have to come to Bolton and they have got to go to Blackburn. It could be difficult for them."
Ruud van Nistelrooy came off the bench to grab the winner against Bolton and become the eighth United player to score 150 goals for the club.
West Ham (h)
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Louis Saha also scored in the win and Ferguson says he has been left with a dilemma about which striker to start with against Arsenal.
"We've got a massive game next week against Arsenal, we're playing well, they're playing well, it should be a fantastic game.
"But if we can just get over that hurdle then we will have a chance.
"We are catching them and we just hope the finishing line doesn't come too soon."
Chelsea boss Mourinho has blamed his side's away displays for their dip in form as he prepares the Blues for their game against London rivals West Ham next Sunday.
"It's obvious that away from home we are not performing the same and we are not getting the same results," he said.
"In the first part of the season we won every match away and last season was the same.
"This season what keeps us in the great position we are is the great record we have at home because at home we do not lose points."