City's defeat at Southampton, coupled with United's victory over another of Reid's former clubs Everton on Sunday, has opened up a 12-point gap at the top with a dozen matches remaining. The former England international does not expect United to be caught believing their ability to win matches when they are not at their best will get them over the line.
"Champions win football matches when they are not playing well," he told Press Association Sport. "Manchester United have done it and Manchester City haven't and that's the bottom line. That is why they are 12 points clear and that is the reason I think they will win it."
City have been well short of last season's form, when they won the Premier League with virtually the last kick of the season, and Reid believes a number of factors have conspired against them.
He said defending the title was tough enough but felt crashing out of the Champions League group stage for the second successive season delivered a significant blow to morale.
"I think it is very difficult to retain a title. Everyone wants to beat the champions," added Reid, speaking at St Helens Junior Football Club who are halfway through the Football Pools 90-Day Community Challenge to complete a £50,000 makeover.
"Vincent Kompany and Yaya Toure, two of their best players, haven't been as influential as they were last year.
"They haven't scored enough goals - they scored a lot last season - and that all comes into the equation.
"In the Champions League they had a hell of a difficult group but they got three points and for the Premier League champions that is a really poor return.
"As a result I think confidence and momentum were lost early on by City as it showed you where they are in the grand scale of things in Europe and that has been borne out in the Premier League. But they have still got the firepower and some really good players."
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