Coleman, who took Stanley back to the Football League in his previous stint, is back in charge following the departure of James Beattie and masterminded only their second league win of the season.
Doubles from Robert Atkinson and John O'Sullivan helped the visitors into a 4-1 lead with 15 minutes to go, but a pulsating finish saw Ivan Toney score twice and Darren Carter strike for Northampton.
Thankfully for Coleman, however, Sean Maguire had scored his side's fifth with the score at 4-2 to secure a sensational result.
Bury are the new League Two pacesetters as they comfortably beat Burton Albion 3-1, with the visitors subsequently losing their place at the summit of the table after a suffering back-to-back defeats.
Carlisle United got off to an unimpressive start to life under new manager Keith Curle as they were beaten 3-2 by hosts Mansfield Town.
The Cumbrians were relegated from League One last term and their miserable form shows no signs of stopping, as they remain bottom of the table without a win to their name.
The two sides promoted from the Conference faced each other, with Luton Town claiming a slender 1-0 win at Cambridge United, who had Tom Naylor sent off early in the second half.
Dagenham and Redbrige avoided a fourth straight league defeat as they drew 1-1 at Cheltenham Town, while high-flying Wycombe Wanderers were held to the same scoreline at Portsmouth.
Southend United continued their strong start with a 3-2 win at struggling York City, but Morecambe suffered a blow as they lost 1-0 at AFC Wimbledon.
Exeter City claimed only their second victory of the campaign as they defeated Tranmere Rovers 2-1 on the road and Plymouth Argyle eased to a 2-0 win over Hartlepool United.
There were also a couple of 0-0 draws, as Oxford United were held by visitors Stevenage and Newport County took a point from Shrewsbury.
