Chelsea were the only one of the top four to lose last weekend and Hartson feels they have now handed the initiative to the 2012 champions.
The Londoners' 1-0 defeat at Aston Villa left them top of the table with 66 points from 30 games, with Liverpool and Arsenal four points further back having played a game fewer.
But City are just two points adrift of the chasing duo with three games in hand and Hartson is convinced that will prove the difference come the end of the season.
Speaking ahead of his golf day at Loch Lomond in aid of the John Hartson Foundation, the Welshman said: "Liverpool are right in there after their win at the weekend.
"That victory put a marker down for them, going to Old Trafford and winning so convincingly, but for me I think Manchester City are in pole position.
"Chelsea have the points on the table and have a massive game against Arsenal this weekend but if I had to say one team today then my favourites right now would be Manchester City because of their games in hand."
And Hartson is refusing to rule out a domestic double for his former club Arsenal, who have not won a trophy for nine years.
"No disrespect to any of the other clubs in the semi-finals of the FA Cup - Wigan, Hull and Sheffield United - but Arsenal must be huge favourites to win that.
"Wigan will be desperate to hang onto the trophy they won last year but Arsenal's players and fans will be thinking they have a serious, serious chance to finally win a trophy.
"They bounced back from a difficult evening in Munich last week to beat Tottenham and that will give them a massive boost ahead of this weekend's trip to Chelsea."
Speaking at the same event, Republic of Ireland manager Martin O'Neill is edging towards Chelsea but admits the final outcome is 'too close to call'.
"Despite what the Chelsea manager is saying right now I think points on the board are very, very important," he told Sky Sports News.
"Last week's turnaround seemed to favour Manchester City but Liverpool are playing so strongly at the moment that you certainly couldn't discount them.
"And Arsenal were big winners too, so I must admit it's very tight, really interesting and too close to call.
"They had a big win at White Hart Lane on Sunday and are right back in the equation. That has given them a massive boost of confidence at the right stage of the season."