CMB were 11 minutes from a potentially pivotal three points after Callum Yearsley’s opener for Matt Taylor’s men.
But Oliver Wilkinson struck a magnificent equaliser from inside his own half before David Lang’s scrambled finish three minutes from time secured a 2-1 win and sparked scenes of bedlam at Gamble Road.
CMB are now four points behind with three games in hand on their rivals and still in the box seat for the title – but are now firmly in a two-horse race.
CMB had the better chances in the first half and had a goal ruled out for a foul on keeper Mark Smith early on.
Obinna Ebizie then headed over as CMB looked dangerous from set pieces while CMB defender Oliver Turner timed a tackle to perfection as Wilkinson bore down on goal after a free-flowing move.
In truth, neither keeper had a save to make as both sides’ neat approach play failed to result in clear chances at either end.
With tension building in the second-half as the stalemate wore on, CMB broke the deadlock, Callum Yearsley’s 25-yard effort squirming over the line.
CMB could have doubled their lead when tricky winger Robbie Deighan pulled the ball back for Dylan Winstanley but the ball was behind him and he could only scoop his effort over the bar.
As the clock ticked down, Thornton needed something special – and Wilkinson supplied it.
After CMB goalkeeper Joe Leather left his goal area to make a clearance, the ball fell to Wilkinson’s left foot with the midfielder striking an inch-perfect effort from almost 60 yards into the net as Leather tried in vain to get back.
Thornton pushed for a winner and it arrived on 87 minutes. Leather brilliantly palmed Wilkinson’s 20-yard free-kick out for a corner but from the resultant set piece, Lewis Walmsley's header crashed off the bar and sub Lang was on hand to bundle the ball home among a posse of CMB defenders.
Even then CMB could have snatched an equaliser in the 95th minute, this time Thornton managing to scramble the ball away to safety on the goal line with Ebizie ready to stab home.
It was a fine advert for the West Lancashire League played in a good spirit and sets up what should be an exciting final few weeks of the season in the top division.
Away from the battle of the top two - and over the fence at Poolfoot Farm - Fulwood Amateurs secured a comfortable 4-1 win at Wyre Villa thanks to goals from Joe Hooper, Yasin Resaei, Jonty McDonald and Spencer Lucas.
Harry Rowe, meanwhile, was the scorer for the hosts.
Rossendale also registered a 4-1 victory, with Scott Wylie scoring twice, and Will Foster and Tom Hulme also finding the net in a triumph over Turton, whose goal came via Ricardo Pembele.
Shane Tyson and Andrew Sinclair netted either side of a Cuan Bradley equaliser as Whitehaven sealed a 2-1 win at Hurst Green.
And it was a case of 'The Generation Game' for Burscough Richmond who also picked up three points on the road, with 40-year-old Lee McNabb and 18-year-old Zach Carberry striking in quick succession to help their side see off Milnthorpe Corinthians 2-0.
Just two Division One fixtures survived the wet weather, with Josh Hill and Ryan Fletcher netting either side of a Jordan Freeman double as Croston Sports won 4-0 at Kendal County.
Meanwhile, Askam United beat Southport Hesketh 1-0, with Will Hindle grabbing the only goal of the game to go second.
Astley and Buckshaw continued to build on their lead at the top of Division Two, with a late Kurt Robinson brace rounding off a 4-0 win at Galgate.
Charlie Oxley and Ollie Vaulks had earlier found the net to secure a result that opened up a massive 15-point cushion at the summit, albeit with the leaders having played significantly more games than most around them.
The division’s biggest win of the weekend, however, was produced by Kendal United, who won 7-1 at Charnock Richard Reserves, with Ryan Close and Jonny Voortman both scoring twice.
Jamie Harris, Matthew Kennedy and an own goal rounded off the visitors scoring, whilst Cole Davies registered a late consolation for the home side.
Goals from Robbie McMurdo and Robbie Sanderson saw Dalton United rally to claim a point at Storeys, that after Joe Wareing had put the hosts 2-0 up inside half an hour.
Tom Knight, meanwhile, scored what proved to be the decisive goal as Pause United beat Stoneclough 1-0.
By contrast, it was goals galore in Division One Reserve, with Poulton Reserves netting no fewer than eight on their way to victory at Rossendale Reserves.
Andy Harvie, Haiden Wrathall and Deontay Atkinson each scored two, whilst Jared Bain and Rob Douglas netted one apiece.
Milan Tinant got the only goal for the home side.
Division leaders Thornton Cleveleys Reserves won 4-1 away from home, with Tommy Dollin and Jordan Rankine finding the net either side of a Harry Johnson double to secure victory over Fulwood Amateurs Reserves, whose goal came via George Lowe.
And Ric Seear was the latest player to score twice as Blackpool Wren Rovers Reserves survived a late scare to win 3-2 at Eagley Reserves.
Seear’s brace, either side of a goal from brother Ben, appeared to have wrapped the game up, before strikes from Kennedy Corvelli and Rhys Hardie, the latter of which came in stoppage time, set up a tense final few minutes.
There was late drama too at Coppull Reserves, where visitors Lostock St Gerards Reserves sealed a 2-1 win with just five minutes of normal time remaining.
Tyler Wane was the scorer of the game’s decisive goal, that after Reece Thompson’s opener had been cancelled out by the hosts’ Greg Brickell.
In one of just two fixtures fulfilled in Division Two Reserve, Dan Blackburn netted a hat-trick and Callum Dickinson scored twice as their Thornton Cleveleys A side won 6-0 at Fulwood Amateurs A.
Byron Greenwood was also on target in the win.
And concluding this weekend’s league action are Hesketh Bank Reserves, who eventually saw off Carnforth Rangers Reserves 4-2 thanks to goals from Jordan Smethurst, David Yeates, Peter Jones and Macauley Levi-Smith.
Kieran Gorton and Carl Holt had given their side hope of an improbable late comeback, but it wasn’t to be, as Levi-Smith struck to swiftly stamp out that possibility.
Turton Reserves do have the final word of this edition, however, after securing their spot in the semi-finals of the Stewart Rowe Memorial Cup.
A Jake Wallbank brace, along with a goal from Tom Hardy, sealed a 3-1 in their last eight tie against Chipping Reserves, whose only goal came via Will Heane.
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