Marc Richards missed a stoppage-time penalty as the Saddlers came from behind to beat struggling Northampton.
John-Joe O’Toole put the Cobblers in front on 23 minutes, but second-half goals from Matt Preston and Erhun Oztumer – his 11th of the season – turned the match on its head.
Northampton had a golden chance to salvage a point at the death, but Richards skied his penalty high over the bar as the Saddlers held on for a third straight home win.
Jon Whitney’s side are now 11th in League One, four points behind sixth-placed Southend, albeit having played a game more.
After a low-key start, the Saddlers almost took the lead with the game’s first chance on 14 minutes.
Erhun Oztumer’s left-wing corner was touched on by Eoghan O’Connell to Matt Preston, whose shot on the turn came back off the base of the post.
But it was the Cobblers – 2-0 winners when the teams met back in September – who drew first blood midway through the half.
Matt Taylor’s wide free-kick was dropped by home keeper Neil Etheridge and hooked in by O’Toole from close range.
The Saddlers struggled to create anything in response.
Jason McCarthy volleyed harmlessly wide from an Oztumer corner and Preston just failed to connect with a Cuvelier free-kick, as Adam Smith in the visitors’ goal remained untroubled.
Half-time: Walsall 0-1 Northampton
Goalmouth incident proved in short supply at the start of the second period.
O’Toole sliced a half-volley well wide from the edge of the area, while Adam Smith raced off his line to gather the ball at a marauding Jason McCarthy’s feet.
The Saddlers found an equaliser just past the hour, Preston sliding in to convert Cuvelier’s in-swinging corner for his first goal of the season.
Northampton could have regained the lead almost immediately, when Marc Richards headed substitute Michael Smith’s delightful centre agonisingly wide of the far post.
And that miss came back to haunt the Cobblers as Walsall went in front on 69 minutes, Oztumer keeping his composure to fire home after Isaiah Osbourne’s initial effort was blocked by Smith.
The hosts’ hard work was nearly undone three minutes later, but Etheridge produced a brilliant diving save to push away O’Toole’s downward header from Taylor’s corner.
Oztumer then curled a left-footed free-kick wide from 25 yards, before the Saddlers somehow survived a massive goalmouth scramble.
Northampton had a golden chance to equalise in the fifth minute of added time, when Adam Chambers tripped Richards inside the box.
The striker picked himself up to take the resulting penalty but blazed his effort high over the bar – as the Saddlers held for all three points!
Full-time: Walsall 2-1 Northampton
Team: Etheridge, O’Connor, O’Connell, Preston, McCarthy, Chambers, Osbourne (Dobson 79’), Cuvelier (Laird 84’), Edwards, Oztumer, Bakayoko (Jackson 62’).
Subs not used: MacGillivray, Morris, Randall, Makris.
Attendance: 4,954 (941 Northampton supporters).