Rubin Colwill's eighth goal of the campaign finally broke the deadlock at Cardiff City Stadium in the 79th minute and confirmed Port Vale's relegation to Sky Bet League Two next season in a 1-0 defeat.
Vale boss Jon Brady said his side would not give up the fight after last weekend's goalless draw against Wigan, but another 90 minutes without scoring sealed their fate.
Port Vale headed to the Welsh capital to face a Bluebirds team which had clinched promotion back to the Championship with a 3-1 triumph at Reading four days earlier, knowing they had to win all of their four remaining fixtures and hope Leyton Orient and AFC Wimbledon failed to pick up any points to survive.
There was little or no meaningful action in the opening 45 minutes, Joel Colwill forcing Joe Gauchi into the only save of the half in the Vale goal.
The home side needed a brilliant save from Nathan Trott three minutes after the restart to keep out a Ben Garrity header from a corner.
Yosef Salech and Joel Colwill had two bites of the cherry in front of goal just past the hour mark before Chris Willock curled a cross to the far post for Rubin Colwill to head home.
