Home debutants Barry Conlon and Martin Gritton both netted vital goals for the second successive Saturday as the league leaders were completely outplayed despite snatching an early lead.
But Walsall still came to close to an injury-time equaliser when substitute Dean Keates' powerful close-range drive was parried by keeper Jason White before captain Jake Buxton completed the clearance on the goalline.
Angry Stags fans stepped up their year-long protests against owner Keith Haslam, chanting non-stop for up to two minutes at the start of each half in an organised protest calling for him to resign.
On the pitch the Stags, who had already claimed the scalps of promotion favourites Swindon and MK Dons at Field Mill, made a bright start with Gritton's low shot drifting wide.
But in the ninth minute the visitors took the lead from their first attack. Martin Butler flicked on a Daniel Fox corner and, as the home defence hesitated, Ian Roper turned the loose ball in from close range.
The home side refused to be down-hearted and should have equalised when Simon Brown's long raking pass put Conlon clear but keeper Clayton Ince came to Walsall's rescue with a fine block as the striker charged on goal.
However, the keeper has no chance a minute later when the new signing smashed in his third goal in only his third game for the Stags, crashing in Stephen Dawson's low left-wing cross from six yards.
Six minutes later and with the home side still dominating, Matt Hamshaw's thunderous cross-field shot grazed the bar and then another rocket shot, this time from Conlon from 20 yards, narrowly flew wide of the post.
The Saddlers had failed to test young Mansfield keeper White in the first half and Swedish striker Par Cederqvist - making his full debut for the league leaders - was withdrawn at half-time.
And his replacement Hector Sam immediately showed his trickery with a great turn and pull back in the 49th minute which Butler almost converted with a stooping header.
The Stags, who lost full-back Johnny Mullins and centre-half Alex Baptiste to injury before the hour mark, shrugged off their defensive problems to take a 58th minute lead.
There appeared to be little danger when Ince rose to collect another Brown cross, but Gritton's tame challenge forced the keeper to drop the ball and the striker tapped in the loose ball for his second goal for the club.