A mistake from goalkeeper Joe Anyon gifted Chesterfield their opening goal and the second half was totally one-sided as the visitors were booed and jeered by their supporters.
The only blot on an otherwise impressive day's work for the home side was an injury to striker Jamie Ward, who could be out for six weeks with a damaged hamstring.
Ward scored the second goal and was a constant threat to a Vale defence which had to be re-jigged when full-back Colin Miles was injured in the warm-up.
But that could not be used as an excuse for such a desperately limp display and manager Martin Foyle kept his players in the dressing room for half an hour after the game.
It is now 18 years since Vale won at Chesterfield and it is unlikely that any of the previous performances were as poor as this.
Chesterfield had not won any of their previous four matches and were only a point above the bottom four, but it was the visitors who looked like a team threatened by relegation.
They did not force Barry Roche into a save until injury time and so many players were below par the only surprise was that Chesterfield did not take the lead until the 38th minute.
They should have been in front earlier when Anyon fumbled a Peter Holmes shot and the ball appeared to cross the line before the keeper recovered.
But there was no reprieve for the keeper when a low shot from Phil Picken slipped through his hands and rolled into the bottom corner.
Vale's front men had not looked like threatening the home defence and the second half was largely played out in the visitors' half.
Somehow Vale managed to hang on but the game was decided when Danny Sonner lost out to Derek Niven and his pass was lashed into the net from the edge of the area by Ward.
Two minutes later the striker was forced to limp out of the game, but Chesterfield continued to create chances and they scored a third in stoppage time when Wayne Allison held off Weston to squeeze a lot shot past Anyon from a tight angle.
Many of the Vale supporters had already left by then, but those that remained made angry gestures towards the players as they trooped sadly towards the dressing room and a lengthy inquest with their manager.