Trinity’s winning streak ended rather abruptly as Chorley smashed four goals passed a defence which had not been breached for two games.
James Dean netted a hat trick for the Lancashire side as the Blues were given a hiding by a side with eyes on a second straight promotion into the Conference Premier.
Trinity named an unchanged line up for the game as they hoped to continued there decent recent form which had seen the Blues win there last two without conceding.
The form was a distant memory rather quickly as Gainsborough found themselves a goal down inside the first six minutes.
It was a return to their poor starts to games this season as a Jack Dorney cross was turned home from three yards by Aaron Burns on his debut for the Magpies.
The goal disorientated Trinity even further as Chorley began a 20 minute period where they battered Jan Budtz’s goal at times.
Minutes after the opener Budtz was forced to tip over a James Dean effort from the edge of the box.
The Lancashire side kept applying the pressure and after 15 minutes Josh Hine broke down the right before he unleashed a strike against the post.
Gainsborough manager Steve Housham responded by replacing centre half Chris Salt after 20 minutes with Jake Picton.
This enabled a period of stability for the Blues as the more experienced Picton added more composure to the back line.
A minute after half-time and the stability was over.
Goalscorer Burns flicked the ball through to Dean and he made it 2-0.
Within 10 minutes the day got even worse as after saving the initial effort from Hine, Budtz brought the midfielder down in the box.
Dean drilled the penalty home to grab a second.
Moments later Dean tapped in a third to bag the match ball.
It had to take four goals to stir Gainsborough as they ended the tie with a bit more respectability.
On loan Hull City striker Johnathan Margetts forced the home keeper into two late saves before being bundled over in the box in the last minute of normal time to win a spot kick that substitute Simon Russell stroked home.
Despite the goal, it was an afternoon which manager Housham wanted to forget.
He said: “It is one game we will put to bed because it was a poor performance all round.”
“We didn’t win any of our battles and the goals we gave away were poor.”
“We are all in this together.”
“Everyone was frustrated and I will deal with that in my own way.”
“The pitch was not great but that is the case for both teams and they dealt better with it on the day.”
Gainsborough Trinity: Budtz, Roma (c), Davie, Dixon, Quinn, Salt (Picton 20), Davis (Yates 45), Toner, Margetts, Beesley (Russell 58), Clayton. Subs: Stamp, Binns.
Gainsborough goalscorers: Russell (pen 90).
Chorley: Ashton, Ross, Mather, Teague ©, Flynn, Roscoe, Hine (Simm 83), Whitham (Winter 77), Dean, Burns, Dorney (Almond 64). Subs: Lynch, Grundy.
Chorley Goalscorers: Burns (6), Dean (46, pen 55, 60).
Referee: Mr A. Backhouse.