Louis Appéré was brought down for a penalty after just 35 seconds and that set the tone for a chaotic afternoon in Hertfordshire. Appéré converted but Danny Rose ensured Boro went into half-time on level terms when scoring against his old club after home boss Steve Evans was sent off.
The game exploded back into life late on as Kieron Bowie seemingly grabbed victory on 82 minutes, only for Alex Gilbey to level after 85 minutes. No matter, just another two minutes had passed when McWilliams finished off a terrific move to secure all three points once and for all. And there was still enough time left for Danny Hylton to see red.
Here are our player ratings from an exhilarating encounter at the Lamex Stadium…
1. Lee Burge
Stevenage have taken shots galore at home this season but not here, managing only seven to Northampton's 14. Just three were on target. He hesitated somewhat for Rose's equaliser but was calm and otherwise decisive, particularly when under pressure from Boro's late bombardment... 7 Photo: Pete Norton
2. Sam Sherring
Missed a big chance to double the away side's advantage in the first-half, or rather he was denied by a very smart stop. Mix up with Burge as Rose levelled but had a good game against difficult opposition until injury forced him off... 7 Photo: Pete Norton
3. Jon Guthrie
Had a big role to play, not only as the captain but also as Northampton's middle centre-back against a physical Boro forward line, and he did it very well. Enjoyed some good, if not always successful, battles with his old team-mate Danny Rose... 7.5 Photo: Pete Norton
4. Akin Odimayo
His first league start for the Cobblers and he looked accomplished and unflustered by the challenge, rarely putting a foot out of place. Naturally could not last the distance having also played in the week... 7 Photo: Pete Norton