McLean drove in a low drive 10 minutes before half-time to give the home side a deserved lead, which they doubled soon after the break through Newton's calm finish.
Ross County pulled a goal back when Steven Saunders' overhead kick found the net with just over 20 minutes to play.
But their hopes of getting back into the game were severely undermined when they suffered two sendings off in the space of five minutes.
Ivan Sproule was shown a straight red card for a studs-up tackle on Marc McAusland before Saunders received a second yellow card for a lunging tackle on the edge of his own box.
St Mirren's numerical advantage enabled them to close the game out and earn what they will feel to be a just result after the original match was abandoned in the second half with Saints leading 2-0.
Even with both sides containing 11 men, Danny Lennon's side had largely dominated the game.
Steven Thompson, Darren McGregor and McLean had all gone close before the latter finally broke the deadlock with a low shot from 18 yards following Paul McGowan's neat lay-off.
Newton looked to have sealed the points when he swept home from the edge of the box after Thompson had shown good strength and awareness in the box to hold the ball up before finding the scorer.
However, County got themselves back into the game in spectacular fashion when Saunders showed superb skill and athleticism to flick the ball up and volley home inside the box following a corner.
Saunders went from hero to villain, though, as he joined Sproule on the sidelines during a spell of indiscipline that completely undermined their attempts to get a point.
The away side left the field aggrieved as the referee denied them what they felt to be a certain penalty for handball against Goodwin.