Second Division leaders Morton stunned Forfar with a four-goal blitz at Station Park. Morton captain Stuart Greacen headed in after seven minutes and he doubled his and Morton's tally in the 31st minute with a close-range effort.
Chris Templeman made it 3-0 in the 59th minute with a shot from just inside the box before Greacen's penalty was saved.
Mark Allison was sent off for protesting the award. Peter Weatherson scored the fourth in the 77th minute.
Forfar: Wood, McNally, King, Allison, Tierney, Lunan, Tade, Moon, Stewart (Tosh 76), Fraser, Gates (Coyle 66). Subs Not Used: A Trialist, Donald, B Trialist.
Sent Off: Allison (68).
Booked: Moon, Coyle.
Morton: Mathers (McGurn 46), Weatherson, Macgregor, Harding, Greacen, McLaughlin (Millar 80), Finlayson, Stevenson, Templeman, McGowan, McAlistair (Linn 72). Subs Not Used: Walker, Russell.
Booked: McAlistair.
Goals: Greacen 7, 31, Templeman 59, Weatherson 77.
Att: 765
Ref: C Hardie