Grimsby came from 2-0 down to deny Colchester a first Sky Bet League Two win of the season as they drew 2-2.
Frank Nouble and Luke Norris had seemingly put the visitors in control, but James Hanson's penalty and Matt Green's late volley earned the hosts a point.
Colchester took the lead against the run of play, with Nouble slamming the ball home in the 25th minute after the hosts had failed to clear it from deep inside their own half.
Nouble was once again involved as he sent the ball to the back post during stoppage time of the first half, where Norris managed to beat a couple of Grimsby defenders to it and head Colchester into a 2-0 lead.
Grimsby immediately hit back in the second half when Moses Ogbu was bundled over in the penalty area, with Hanson burying his 48th-minute penalty with aplomb.
Colchester appeared to be heading for victory, but Green struck in the 87th minute with a sweetly struck volley to earn Grimsby a hard-fought point.