Williams was signed on loan from Colchester for the rest of the season just 24 hours earlier.
He was brought on after 56 minutes by Seasiders manager Simon Grayson who had seen his side totally lack any impetus in front of goal.
Williams turned that around and with one of his early touches set John Murphy free and the big striker lashed a shot against the bar.
The ball ran clear to Williams who twisted one way and then another before letting fly past Mark Goodlad.
Before that it was almost all Vale as they mastered a swirling wind and heavily sanded pitch far better than Blackpool.
Vale's problems came in front of goal where Michael Cummins was guilty of three bad misses.
However, even those were not as bad as the one from Tony Dinning in the 75th minute.
He lashed his penalty kick two yards wide of the post after Marc Joseph had been rather harshly judged to have handled when the ball flew up from the rutted surface.