Ramsbottom marched into the top six following a convincing win over lowly St Helens Town.
Goals Chris Steele, McManus and Carl Lomax ensured Lee Sculpher's in-form team completed a league double over the Merseysiders for the first time in the club's history.
The Rams started brightly and had appeals for an early penalty when Carl Lomax's free-kick appeared to strike the hand of a Town player, but the referee waved play on.
But the visitors did not have to wait long for the opening goal after McDonald was fouled just outside the box on 21 minutes. Steele's free-kick looped over Town goalkeeper Graham McCall.
Ramsbottom doubled their advantage before half-time when, following a quick counter-attack, McManus found himself in space on the left side of the area.
His cross into the box was a poor one which McCall was expected to deal with, but the keeper misjudged the bounce and the ball slipped between his legs to hand United a timely boost before the break.
The game was effectively over six minutes after the restart when McCall again was at fault when he allowed Lomax's free-kick to slip through his grasp for another soft goal.
Town grabbed a consolation through Lee Thompson on 75 minutes, but their joy was short lived as John Elias was sent off moments later following a late tackle on Steele which warranted a second booking.
The Rams travel to Glossop North End on Saturday (kick-off 3pm).
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