Steven Schumacher put Boro ahead half-way through the first half but Calvert-Lewin and then Alfie Potter scored on the 49th and 64th minute to send the home side on their way to victory.
Teddy Sheringham made three changes to the side that drew at Portsmouth earlier in the week, Chris Whelpdale coming in for Ben Kennedy, Tom Conlon coming in for Dipo Akinytemi whilst an injury to Dean Parrett saw Steven Schumacher return to the side as captain.
Northampton started the game on top and used the windy conditions to their advantage, testing the Boro defenders as much as possible with balls into the box. The hosts had nine first half corners and Joronen had to have his wits about him on the ninth as it looked to be heading in but for a fine, scrambling save.
Boro weren’t able to show much going forward in the early exchanges but made their opportunity count on 24 minute when Steven Schumacher burst into the box before hammering it past the keeper with the help of a deflection.
Now 1-0 up, Boro looked to press home the advantage and Schumacher could have got his second moments later, unable to steer a back post header into the net from close range.
A number of half chances came and went for Boro before the golden opportunity to make it 2-0. Michael Tonge was taken out by the touchline before playing the ball down the line for Okimo. The referee played on, Okimo crossed for Whelpdale who got a touch on it from a few yards out but couldn’t turn it in.
Boro went into the break knowing that they had the better of the half but only the one goal.
As the second half got underway, it was the home side that looked the most likely to score and it didn’t take long before they did - Calvert-Lewin managing to steer the ball home through a busy box after a great ball across from Buchanan.
Whelpdale and Gnanduillet had half-chances to retake the lead but good defending thwarted them both before Potter, only on a matter of minutes made it 2-1. After Calvert-Lewin poked his shot past Joronen, McCombe was unable to clear it off the line and Potter forced it into the net.
The home side continued to look dangerous and Richards should have done more when Northampton found themselves with a three-on-one advantage in the final third. The top scorer dragged his shot at Joronen who gathered easily.
It should have been 2-2 on 69 minutes as a neat passing move released Fraser Franks into the box, the defender unable to hit the target though as it flew wide of the far post.
There wasn’t much from either team in the remaining of the game, Boro struggled to break down the home team and Northampton looked dangerous on the counter without creating much. It was a desperately disappointing second half after a first with so much promise.