Hibernian suffered a surprise defeat as Morton dented the Easter Road side’s hopes of automatic promotion.
Thomas O’Ware’s header and strikes by Denny Johnstone and Ross Forbes ensured Alan Stubbs’ side remain eight points behind Championship leaders Rangers.
Jim Duffy’s visitors, meanwhile, moved to within a point of the promotion play-off places.
Jason Cummings had Hibs’ best chances, including a close-range header in the first half.
Few saw the result coming with Morton having last won a league game at Easter Road in 1982.
Missed chances cost Hibs
Stubbs made seven changes from the side that beat Alloa Athletic on Sunday; but Lewis Stevenson kept his place and was made captain, playing his 300th game for the club under his eighth manager.
Duffy gave a debut to Celtic loanee Paul McMullan, who had been with St Mirren earlier this season.
Before the match, Stubbs said the fixture came under the ‘must-win’ category, and from the kick-off his players seemed to be underlining his message, taking the game to the Greenock side.
The passing was slick, they were patient in possession and Hibs came close on a number of occasions in the early stages through Kevin Thomson with a sizzling shot, Cummings with a header and two inventive efforts from Stokes.
John McGinn even netted, only to be judged offside, and there was a ridiculous miss from Cummings when he nodded past the post from around two yards out.
But Morton weathered all of that and began to create their own pressure.
Mark Oxley had to produce an alert piece of goalkeeping following an O’Ware header and it became clear that, from the home side’s perspective, the evening may not be quite as straightforward as some might have imagined.
Their fears were confirmed when Forbes’ whipped corner from the right was met by a courageous header by O’Ware, who attacked a crowded area and forced the ball home.
Easter Road, bar for 100 or so joyous travellers from Greenock, was silenced.
Suddenly it was all change. Morton looked energetic and creative, Hibernian nervous and predictable. They looked like they craved the half-time advice of their manager.
But whatever Stubbs said had no effect. In fact it went from bad to worse when Morton doubled their lead shortly after Stokes claimed unsuccessfully for a penalty following a challenge by Forbes.
Declan McManus delivered a hopeful cross and Oxley made a dreadful hash of dealing with it, spilling to the feet of Johnstone. It was a tap-in job and Hibs were deep in trouble.
Bobby Barr thundered down Morton’s left on the counter-attack and delivered a telling pass for Forbes to produce a sweeping finish into Oxley’s net.
It rounded off a stunning performance by the visitors and one which left the Hibs fans looking on in disbelief.