A bizarre second half flare up at the Proact cost Chesterfield the services of Dion Donohue, the match, their composure and their unbeaten run.
Spireites defender Sam Hird got tangled up in the celebrations of Walsall’s second goal, leading to a melee that brought a red card for Donohue, and eventually a 4-1 defeat for Danny Wilson’s men.
It was a spectacular return to form for the Saddlers, previously winless in six, and a disappointing conclusion to Chesterfield’s five-game unbeaten streak.
In part, Chesterfield were architects of their own downfall – Tom Anderson, so solid defensively in recent outings, scoring an own goal and gifting Walsall another with a slip.
The Saddlers did play some nice stuff, however, especially after the break, albeit assisted by their numerical advantage.
Before that, there wasn’t much at all between the sides, one of whom has hopes of automatic promotion, the other seeking to protect their League One status.
Walsall came out full of intent, dominating the opening 10 minutes and creating a couple of good chances, Tom Bradshaw’s header drifting over Tommy Lee and past the post, Rico Henry seeing a shot tipped wide of the upright.
With a quarter of an hour gone the Spireites broke out of their shell, Jay O’Shea at the heart of most of their purposeful attacks.
The winger dragged the hosts up field and after patient build up, got back on the ball to curl over the bar from the left side of the box.
A minute later the Spireites should have gone ahead, O’Shea’s scoop over the top of the defence finding Novak all alone six yards out, but Neil Etheridge got down to block at his feet.
It was no surprise that the opening goal came through O’Shea’s endeavour, his floated cross into the area tempting Etheridge off his line, only for centre-half James O’Connor to get in the way and bundle the ball into his own net.
It took Walsall time to settle again after they went behind – Gary Liddle’s niggling, physical interventions – all of them legal in the eyes of referee Ross Joyce – stopping the Saddlers from playing in key areas.
He kept a tight rein on Romaine Sawyers, who was unable to pull the strings for the visitors.
But when the playmaker did get time on the ball, it resulted in a chance for Jordy Hiwula, who shot tamely into Lee’s arms.
Walsall’s leveller, 10 minutes before half-time, was reminiscent of the goal they conceded, Mantom’s dangerous cross forcing Tom Anderson into a hurried clearance that he could only slice into his own net.
The second half was 12 minutes old when it exploded to life, and took two turns for the worse for Chesterfield – Sam Mantom stroking a calm finish into the corner of the net from 18 yards, before all hell broke loose.
As Walsall attempted to celebrate, a huge melee broke out - the result of which was a red card for Donohue, who appeared to go head first into the scuffle, and yellows for Hird, Banks and Mantom.
Only the reactions of Lee kept Spireites in it shortly after the sending off, the goalkeeper flinging himself down to bat away Rico Henry’s downard back post header.
But the goalkeeper was left stranded when Anderson uncharacteristically miscontrolled 25 yards out, allowing Hiwula to stroll through and finish for a 3-1 lead.
With a quarter of an hour to go the Saddlers wrapped it up, and sent droves of Chesterfield fans home early, a slick passing move unlocking the home defence for Mantom to go through and find the net.
Chesterfield’s chances had gone, along with Novak’s composure, the striker’s frustrating afternoon ending in a booking for dissent.
Soon after he made way for Ritchie Humphreys, still fuming as he crossed the touchline, a strenuous 80-minute effort unrewarded.
There was little more in the way of goalmouth action, save a Humphreys stab that sailed wide after good work from fellow replacement Sylvan Ebanks-Blake.
And the travelling support threw a dig or two in the direction of their recently departed manager, as they celebrated an emphatic, dramatic victory.
Chesterfield: Lee, Talbot (John 69), Donohue, Anderson, Hird, Liddle, Ariyibi, Banks, Dimaio, Novak (Humphreys 79), O’Shea (Ebanks-Blake 73). Not used: Chapman, Simons, Raglan, Slew.
Walsall: Etheridge, Downing, O’Connor, Taylor (Forde 79), Demetriou, Henry, Chambers, Mantom (Morris 88), Sawyers, Bradshaw (Lalkovic 84), Hiwula. Not used: MacGillivray, Lalkovic, Preston, Flanagan, Kinsella.
Referee: Ross Joyce.
Assistants: Graeme Fyvie, Tom Nield.
Fourth official: Joe Hull.
Goalscorers: Own goal 19; own goal 35, Mantom 57, 75, Hiwula 71
Yellows: Banks 56, Hird 57, Novak 69; Mantom 57
Red: Donohue 57
Attendance: 6,938 (823 away)