Day pulled away from the chasing back after a run of three successive birdies on the back nine, but failed to hold his nerve at the crucial moment.
Successive bogeys at 16 and 17 pushed Day out of contention, leaving Cabreba and Scott to battle it out for the famous green jacket at the final hole.
Scott looked to have done enough after scoring a birdie at the 18th with a terrific putt from 25 feet to move clear at nine under, but Cabrera battled back again to set up his own birdie chance at the last with superb approach play.
Cabrera stayed calm to force a playoff with a short putt, leaving the Argentine and Scott needing extra holes to decide who claims the title in Georgia.
You can follow live text commentary of the playoff with Sports Mole's minute-by-minute coverage by clicking here.