Vale slumped to a miserable defeat, blowing a chance to go 4th.
Vale welcomed Stevenage for the first time ever in the league by gifting them a 1-0 lead. A backpass from Anthony Griffith hit a bump and slipped gently past goallie Chris Martin on the half hour.
Vale promptly fell apart allowing Peter Winn to thump home a second goal 7 minutes later, with Vale failing to clear a Lawrie Wilson cross.
Vale finally pulled one back on the hour, although Sam Morsy's shot was so deflected it was hard to see how he could claim it.
But Stevenage made it 3-1 when David Bridges tapped in the rebound off Martin's save from Ronnie Henry's shot.
The fans voted Martin man-of-the-match by text, but it's a game he won't want to remember.
Vale remain 6th.