Gainsborough thought they had taken the lead inside the first ten minutes but an assistant’s flag ruled out the effort.
It became 1-1 on disallowed goals with Chasetown’s Levi Rowley stooping to net, ruled out by a foul on keeper Jonathan Stewart.
A minute before the break, Danny Cocks drew a foul outside the area and his resultant free kick was headed over by Jack Langston.
Trinity took the lead a minute into the second half. A lucky break from a Jack Partridge tackle rebounded to Alex Byrne who side footed past Curtis Pond.
Gainsborough almost immediately added a second goal. A loose pass found Simon Russell whose curling effort was superbly palmed wide by Pond.
Chasetown deservedly levelled in the 52nd minute. Jake Lovatt's pass was inch perfect for Levi Rowley who netted his first Chasetown goal with a crisp finish.
Leading scorer Langston was a whisker away in the 76th minute. Keeper Stewart scuffed a clearance and Langston’s 40 yarder was no more than 6 inches wide.
Both sides gave it their all but neither side could force the win and a Tuesday night replay is required.
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