Colchester keeper Sam Walker denied both Charles Vernam and James Berrett early on and Grimsby came even closer to scoring midway through the first half when Karleigh Osborne’s volley clattered the crossbar.
Walker held Luke Summerfield’s close-range header on the line, before Grimsby took a 38th-minute lead when Vernam clinically side-footed home from the edge of the area after Paul Dixon had latched onto substitute Scott Vernon’s flick-on and picked him out.
Walker foiled Vernam again before the break but Colchester equalised less than two minutes after half-time when Sean Murray lashed in from the edge of the area, after Drey Wright had found him following substitute Courtney Senior’s trickery.
Walker brilliantly denied Vernam, while Grimsby’s Ben Davies wastefully headed Berrett’s cross wide unmarked at the far post.
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