Serge Makofo grabbed the only goal as non-league Grimsby shocked Port Vale to advance to the second round of the FA Cup at Blundell Park.
The winger pounced in the 59th minute to fire the Blue Square Premier strugglers through after a thrilling encounter with their League Two visitors.
Makofo buried a low strike into the bottom corner from the edge of the area to see off Vale and secure Grimsby a trip to Salisbury.
The night began ominously for Vale, who were forced to wear an old red Grimsby away strip after a kit clash, and almost got worse when Mariners striker Liam Hearn missed a golden opportunity to fire the hosts into the lead.
He capitalised on a poor backward header by Vale's Lee Collins but shot wastefully straight at grateful keeper Chris Martin.
The Valiants responded when good work by Sam Morsy found Louis Dodds in the box and Town stopper James McKeown had to be alert to keep out his shot with his legs before Morsy struck the post.
The final chance of an even first period again fell to Hearn, who blazed over the bar to the dismay of the home supporters.
After the break Vale went close through John McCombe and Dodds before Makofo's decider.