Ten-man Forfar stayed top of League One despite losing their eight-game unbeaten league run on Saturday at Cappielow.
The warning signs were obvious after 15 minutes when teenager Jon Scullion flicked the ball to his left for Robbie Crawford to drive a first-time low shot on goal from 15 yards but goalkeeper Rab Douglas got down smartly to save.
The Loons went a goal down one minute later when Scullion, making his first start for the Greenock side, pounced on a loose ball 19 yards out and fired in a low left-foot shot, which took a wicked deflection off Ton’s Crawford.
Dick Campbell’s side failed to get a shot on target in a dismal first period until four minutes from the break, when Gavin Swankie cut inside on the left, but goalkeeper Gaston got down sharply to save at his right hand post.
Morton wrapped up the points in 62 minutes when Scotland under-21 call-up Declan McManus whipped in a low cross from the left for Andy Barrowman to slide in and score from eight yards.
Hopes of a revival were blighted when Gaston made another stunning stop from Swankie after 74 minutes.
Forfar were reduced to 10 men in 89 minutes when Jim Paterson saw red for an elbow on Jordan Allan.
Loons boss Dick Campbell was not too downbeat about the defeat.
He said: “We’re still top of the league. You would have to say Morton deserved their victory. The first goal took a deflection and the second goal was a sclaff.
“The sending-off was never a sending-off in a million years. I felt sorry for Jim Paterson, the boy went down like a venetian blind.
“If that’s a sending off, I’d be sent off in the warm-up.
“Two minutes before it, Darren Dods came off with blood coming from his ear, and the linesman never saw it.
“Some of the critical decisions I couldn’t believe. It was petty, petty refereeing.
“We created five magnificent chances. It’s the first time we’ve not scored in a league game.”