Portadown's slim title hopes suffered a massive blow after bottom club Carrick clinched their first home win of the season at the 18th attempt.
Shane Dolan put Rangers ahead from a penalty awarded for a push on Paul Heatley, who collided with perimeter fencing and sustained a gashed leg.
Ian West headed in to make it 2-0 and Gary Breen stabbed home to pull one back for an understrength Ports side.
David Bell's superb 35-yard strike on 71 minutes sealed victory for Rangers.
Portadown were missing nine first-team players and it showed as Carrick threatened in the first minute.
Heatley was denied by keeper David Miskelly after 23 seconds while Ports midfielder Richard Clarke saw his shot fly just over.
Miskelly came to his team's rescue again to keep out a Marcus Kane effort.
Gartland made the push on Heatley which took the midfielder off the pitch and into fencing, causing a leg injury which resulted in the player being taken to hospital.
Dolan despatched the resulting spot-kick before West, the substitute for Heatley, headed home at the far post from Kane's cross after 52 minutes.
Breen gave the Ports hope on the hour mark when he connected with Gartland's nod across goal from a Shane McKinney free-kick.
Bell's spectatular long-range shot and goal of the season contender left Miskelly motionless and eased Carrick nerves.
Ports striker Matthew Tipton just had keeper Paul Murphy to beat late in the game but his weak shot was easily saved.
Portadown remain nine points behind leaders Linfield, who have a game in hand, while Carrick stay bottom but are now within a point of Glenavon.