Colchester stifled an in-form Grimsby side to make it back-to-back wins for the first time this season with triumph at Blundell Park.
Goals from Kyreece Lisbie and Micah Mbick turned the game around for the U's after Kieran Green had headed the home side in front early on.
The visitors threatened in the opening minute as Mbick went through on goal but goalkeeper Christy Pym denied him.
It was free-scoring Grimsby who went ahead in the 17th minute, Green heading in at the near post from a Charles Vernam corner.
Colchester got back on terms in the 38th minute, also from a corner, following an almighty scramble in the six-yard box which eventually led to Lisbie knocking the ball over the line.
The away side flipped the game on its head by the hour mark, with Mbick lobbing Pym from the edge of the box.
Grimsby substitute Jude Soonsup-Bell hit a post with a header deep into stoppage time, with Colchester just holding on.
Match report supplied by PA Media.
