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McCombe strikes to keep Robins top
Carle: Fends off Holland challenge
Darren Ambrose had fired Charlton into an early lead as Alan Pardew's men attempted to close the gap on their opponents to six points.
City, who hit the top spot on Saturday, looked set to become the latest side to suffer a bout of altitude sickness at the top of a division in which no one seems able to hold onto the lead.
But centre-half McCombe - who had not scored all season until a fortnight ago - struck again to keep Gary Johnson's surprise package on top of the pile and a step closer to the Premier League.
A draw also put a huge dent in Charlton's fading hopes of automatic promotion, although it could have been worse after Michael McIndoe struck the woodwork late on.
The hosts went ahead in the eighth minute when Zheng Zhi and Kelly Youga combined well on the edge of the area to play in Ambrose, who coolly tucked the ball beyond Adriano Basso from 12 yards for his ninth goal of the season.
City regrouped and managed to take the sting out of the Charlton attack, albeit belatedly, but were toothless going forward in the opening period.
Dele Adebola looped a header onto the roof of the Addicks' goal from McIndoe's cross, the robust frontman taking a whack to the head for his troubles which required a bandage.
Charlton could have doubled their advantage on the half-hour when Chris Iwelumo rose highest to meet Ambrose's corner, but the big striker planted his header straight at Basso.
As the interval approached Basso crashed a clearance straight at the onrushing Luke Varney, but the visiting keeper was able to clear the danger.
And in first-half stoppage-time Jerome Thomas squandered a gilt-edged chance when he blazed Iwelumo's knockdown wide from 15 yards.
Johnson threw on top scorer Darren Byfield at the start of the second half, and McIndoe immediately hooked a decent chance over the top.
Nick Carle shot straight at Nicky Weaver and McIndoe fired narrowly wide with Charlton suddenly on the back foot.
But City were nearly undone by a horrible error from McCombe, who looped an extravagant backpass towards Basso without noticing he well off his line, forcing a hasty retreat and a headed clearance from the keeper.
Holland then almost bundled the ball over the line after Iwelumo made a nuisance of himself in the area, McCombe this time getting back to clear.
But it was City who made the vital breakthrough just after the hour mark when McCombe rose unmarked to nod Lee Johnson's left-wing corner past Weaver.
The game was then briefly halted when a flare was thrown onto the pitch from the City end.
And McIndoe came agonisingly close to securing City's first win at the Valley in 40 years when his curling 25-yard free-kick beat Weaver and cannoned back off the crossbar.