Saints were leading 2-0 a fortnight ago when the original game was abandoned in the second half because of a waterlogged pitch and were back in front with the same scoreline with strikes from their Scotland Under-21 playmaker and his fellow midfielder either side of the break.
County defender Steven Saunders pulled a goal back before Ivan Sproule was shown a straight red card by referee William Collum for a challenge on Saints defender Marc McAusland and Saunders joined him inside after picking up two quick bookings for challenges, the first on John McGinn, the second on McLean.
With their fourth win in five games to take them into eighth placed, St Mirren's rejuvenation continues while County's third successive defeat leaves them in 10th place although they may feel they were denied a late penalty claim when Saints skipper Jim Goodwin appeared to handle in the box.
After a comprehensive 4-1 home defeat to Celtic last week, County boss Derek Adams made three changes to his team with Sproule, Saunders and Kevin Luckassen in and Mihael Kovacevic, Mark Klok and Carey dropping to the bench.
Buddies boss Danny Lennon kept faith the same 11 which started the 3-0 win over Partick Thistle last week, with Steven Thompson, who grabbed a brace in Maryhill, leading the line and he came closest to breaking the deadlock the scoring during a scrappy opening.
In the seventh minute Newton sent right-back Jason Naismith down the right and the former Dundee United and Rangers striker was first to react to the cross, sending a right-footed effort from eight yards just wide of the target.
It was a fine move somewhat out of place amid the rough and ready football on display.
The Paisley side were slightly the more enterprising and in the 20th minute McLean ended a brief spell of pressure by curling a shot from 20 yards just over the bar.
The game stuttered along with no great cohesion before McLean picked up a Paul McGowan pass at the edge of the box and drilled a right-footed shot low past County keeper Mark Brown for his fourth goal of the season.
St Mirren, who went into the match with three wins in their last four games, were value for their lead and almost doubled it two minutes from the break when, with the visiting defence sleeping, Thompson latched on to a McLean corner but his volley slipped inches past the far post.
However, the second goal was only delayed until five minutes after the break after another cross into the box by Naismith.
Thompson took possession and was allowed to hold the ball up in the County box all too easily before laying it back to Newton who guided a shot past Brown from the edge of the box.
County looked as if they lacked the belief to come back.
In the 61st minute Thompson forced a save from Brown with a flicked header from a McLean cross and it looked all too easy for the Paisley side.
However, in the 66th minute the visitors were back in the game when the St Mirren defence failed to clear a corner from substitute Graham Carey, on for Stuart Kettlewell, and Saunders knocked it into the net from six yards.
Sproule's dismissal two minutes later for a reckless challenge on McAusland in the middle of the park, however, dampened down prospects of a comeback and then two quick bookings for Saunders left County playing out the final stages with nine men.
As St Mirren pushed for number three, Brown made saves from Sean Kelly and Newton before the latter fired just over the bar.
However, the closing moments were fraught and the Highland side appeared to have a good claim for a penalty in the final minute when Jim Goodwin appeared to handle in the box in his attempt to clear but none of the officials spotted it.