Galway United took all three points thanks to a late Stephen O’Donnell penalty at Dalymount Park.
Karl Sheppard fired the visitors ahead on 16 minutes before Raffaele Cretaro slotted in the equaliser for Bohs on 22.
Sheppard headed in his second on 50 minutes and Jason Byrne looked to have taken a point for Bohs with a second equaliser(76) before the added time penalty sealed the win for Galway.
Ken Oman was red carded in added time before Cretaro and O’Donnell received their marching orders following a fracas on the full time whistle.
Following a fairly low key opening Galway snatched a dramatic opening goal on 16 minutes.
Shambolic defending by Bohs after a Paul Keegan ball across the park allowed Declan O’Brien get a touch and Sheppard to pounce on the loose ball on the left and fire nonchalantly past the advancing Bohs goalkeeper Barry Murphy.
Galway were only in front for six minutes before Bohs got back into the game on 22 minutes.
Keegan’s cross from the left of the area was too high for Byrne in the box but it was perfect for Cretaro.
The former Sligo Rovers man chested the ball down and stroked a calm shot past Barry Ryan into the bottom right corner of the net.
Two minutes later Galway had a chance to get back in front when referee Damien Hancock awarded them a free kick to the left of the area, 25 yards out.
Stephen O’Donnell took the free and got a lot of power in his effort but only managed to smash the ball high over the bar.
Both sides had further chances as the half progressed but they went in for the break level.
There was a delay to the start of the second half after assistant referee Martin Maloney felt unwell at half time and received oxygen in the dressing room.
Fourth official Richie Winter took over Maloney’s flag and ran the line for the second period whilst Bohemians kit-man Colin O’Connor replaced Winter.
Bohs went close to a second on 47 minutes when Conor Powell passed down the middle to Byrne who turned and shot but his strike went over the top.
Instead it was United who went ahead on 50 minutes when Sheppard met Seamus Conneely’s free from the wing and nodded the ball past Murphy at his near post with the static Bohs defence maybe expecting an offside flag.
Bohs boss Pat Fenlon reshuffled his pack, introducing Ruaidhri Higgins for Glenn Cronin and later, Mark Quigley for Paddy Madden.
The rejigging and freshness did the trick and they were level on 76 minutes when Powell sent in an exquisite ball from the left for Byrne who flicked past Ryan.
Bohs then enjoyed a great spell of pressure. Ryan made a cracking save from Keegan on 80 minutes before Quigley headed over on 81.
Byrne tried an audacious chip over Ryan on 82 but didn’t get enough on the ball and knocked it into Ryan’s hands.
Oman took down Sheppard in the fifth minute of added time and O’Donnell made no mistake with his spot kick at the Shopping Centre end of the ground.
Oman then received a second yellow card and was sent off and was joined by Cretaro after a foul on Sheppard and by O’Donnell following a fracas after the final whistle.
Bohemians: Murphy; Heary, Powell, Cronin (Higgins 58), Shelley; Oman, McGlynn, Keegan, Cretaro; Byrne, Madden (Quigley 73).
Galway United: Ryan; Conneely, Creaney, Meynell, Sinnott; Ryan (King 83), Foley, O’Donnell, O’Brien (McBrien 88); Sheppard, Flood.
Referee: D Hancock