Riding on a wave of emotion surrounding coach Darrell Clarke, who was absent for six weeks of the season owing to a close family bereavement, Vale easily accounted for Clarke's former club, and was 2-0 up even before Mansfield's Oliver Hawkins was sent off after receiving a second yellow card from Australian referee Jarred Gillett inside 35 minutes.
Teenager Kian Harrett scored Vale's first, nodding in from close range moments after he'd hit the post with a sublime shot from distance.
Vale's second also came from a header, four minutes after the opener, when Jame Wilson was quickest to react after an initial header came back off the Mansfield Town crossbar.
Mansfield should have been ahead before any of that happened, but Jamie Murphy headed straight at Port Vale goalkeeper Aidan Stone after a defensive mix-up when scoring looked easier, spurning an early opportunity to set the tone of the match.
Hawkins's dismissal was completely justified and left Nigel Clough's side with a mountain to climb, but Rhys Oates almost provided hope on 41 minutes when he pounced on a spilled set-piece from Stone. But Connor Hall just managed to clear the ball off the Vale line before it crossed for a goal, the goal decision system confirming it had about a millimetre left to roll before a goal would have been awarded.
A second half with 10 men was always going to be a challenge for Clough's men, but they battled valiantly on, creating a couple of chances. But Vale exerted its dominance for much of the second period and sealed the result – and promotion to League One with it – when Mal Benning volleyed home David Worrall's right-wing cross with just five minutes left on the clock.
