The Northern Premier League team belied their lowly placing in their own league to produce a performance full of aggression and desire and deserved their shock victory.
They were, however, helped by a red card which reduced the Magpies to 10 men on the hour when the tie was finely poised at 1-1.
The hosts should simply have done better after making a flying start with a quality goal in the second minute.
Adam Blakeman put in a fine cross which Marcus Carver headed back across the box for Matty Hughes to rifle an unstoppable shot into the roof of the net.
It could quickly have been 2-0, as Carver’s close-range header was booted off the Marine line. But the visitors were showing attacking intent themselves and Matt Urwin had to tip over a short-range header before Marine equalised in the 17th minute.
A centre from the left was cleverly dummied, allowing the ball to run to Adam Hughes who fired past Urwin from eight yards. Although Chorley fashioned several dangerous raids, from one of which Hughes shot wide when well placed, Marine were being allowed too much room in midfield where the Magpies were badly missing a no-nonsense ball-winner.
Only a superb reflex save by Urwin following a slalom dribble by Danny Mitchley kept Chorley on terms at the break.
The turning-point came when Josh Wilson contested a 50-50 ball in midfield, the collision leaving the two players needing treatment on the ground.
Leicestershire referee Amy Fearns deliberated at length with her assistant before sending Wilson off.
From then on, the visitors gained extra momentum but they were gifted the lead on 74 minutes when Josh O’Keefe unaccountably turned a low centre into his own net.
Yet Chorley had two clear chances to equalise. Carver completely missed an attempted header from Hughes’ pin-point centre, then Andy Teague saw a well-directed header bounce out off the inside of the far post.
As the clock ticked down, the home defence was exposed more than once by quick Marine breakaways and it was no real surprise when, in the fourth of five added minutes, Mitchley totally unmarked swept home a low cross from the right.
With feelings now running high in a fractious finish to proceedings, Marine assistant manager Tony Sullivan was sent off after an exchange with the home bench.
CHORLEY: Urwin, Challoner (Roscoe 84), Blakeman, Teague, Leather, O’Keefe, Haughton, Wilson, Carver, Walker (Whitham 73), Hughes. Subs (not used): Jordan, Black, Jarvis.