Few in a superb Victory Park crowd of 1,675 could have imagined at half-time the outcome of this contest.
The visitors had looked a class act in the first half with their fluent and pacey attacking and might have led by more than the one goal at the break.
But not for the first time this season, Chorley turned up the heat in the second half and seized control, running in four quality goals to light up a gloomy January afternoon.
Matt Urwin was called into action early to parry a wickedly swerving 25-yards drive, Scott Leather coming to the rescue as the loose ball spun back perilously close to the goal-line.
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In retaliation, Josh Wilson saw a good header from a Chorley corner cleared off the line but the Robins were soon causing problems again.
Josh Hancock rattled the bar with a thunderous free-kick, moments before Altrincham took the lead on 23 minutes.
The diving Urwin again did well to push aside John Johnston’s powerful strike but Max Harrop was on hand to fire the loose ball into the far corner.
Chorley missed a couple of presentable chances to equalise but again Altrincham went close as Simon Richman’s fierce shot skimmed the bar.
The second half produced a complete transformation of fortunes. The slickest of one-touch build-ups enabled Alex Newby to tuck away the equaliser on 54 minutes and 10 minutes later Chorley were in front.
Marcus Carver slid a low ball diagonally across the six-yards’ box and Josh Wilson at the far post thumped it high into the net.
As the Magpies sought to finish the contest, Tony Thompson made a brilliant save from an Elliot Newby pile-driver before his brother Alex bagged his second and Chorley’s third six minutes from time.
The build-up featured a ballooned connection by Adam Blakeman but when the ball dropped Newby calmly stroked it through a crowd of players into the corner of the net.
There was still time for the outstanding Courtney Meppen-Walter to put the icing on Chorley’s cake just before the final whistle as he met Blakeman’s well-flighted corner with a towering header which flashed past Thompson.
Manager Jamie Vermiglio confessed to frustration at his side’s first-half display: "I told the boys that if we are going to win the league we can’t perform as we did in that first half. But in the second half we were fantastic, first to everything and comfortable on the ball, and we scored some great goals.
"I’m delighted with the camaraderie the lads showed in getting on top of a very good Altrincham side."
CHORLEY : Urwin, Challoner, Blakeman, Teague, Leather, Meppen-Walter, A.Newby, O’Keefe (Cottrell,69), Carver, Wilson (Hooper,87), E. Newby. (Whitham, 90). Unused subs. Baines, Eccles.