The Spireites certainly had plenty of possession but for long periods failed to penetrate.
They also suffered from having three first-choice central defenders missing and Paul Merson took full advantage as he set Walsall on their way to a first win in five matches.
It was from the player-manager's half-cleared corner that they took the lead in the 14th minute, with Darren Wrack firing home a left-foot shot from 20 yards.
Chesterfield were really caught napping in the 26th minute as the Saddlers increased the lead.
This time Merson took a quick free-kick and with the visitors standing still, Jorge Leitao scored with a fine diving header.
Chesterfield manager Roy McFarland was forced to make changes and brought on giant striker Caleb Folan for midfielder Gareth Davies.
Walsall had a hatful of chances at the start of the second half, but Michael Standing, Leitao and Matt Fryatt all failed to take advantage.
Marvin Robinson came on as a 64th minute substitute for Leitao and was set up by Merson two minutes later, but somehow fired wide of the far post.
Mark Hudson's 20-yard drive was blocked by the alert Neil Emblen in the 71st minute and a minute later Murphy made the first of those outstanding saves - although it has to be said that Folan should have done much better with a close-range header from a cross from Alex Bailey.
In the 73rd minute McFarland made another substitution, bringing on striker Mark De Bolla for the tiring Wayne Allison.
With Chesterfield still pressing it was De Bolla who brought another fine save from keeper Murphy.
As the game went into added time Chesterfield were caught on the break and Merson again showed his expertise by setting up Fryatt to complete the scoring.