Shamrock Rovers cut the gap between them and third-place Waterford FC to four points with victory at a sun-soaked Regional Sports Centre on Sunday afternoon.
Substitute Gary Shaw grabbed the game's only goal 15 minutes from time to narrow the gap between the sides and put a small dent in the Blues hopes for European football next season.
Waterford boss Alan Reynolds welcomed back top-scorer Courtney Duffus and Stanley Aborah following their draw with Bohemian FC earlier this month while the Hoops made five changes to the team who started Thursday's European tie in Stockholm, with Alan Mannus coming in for 16-year-old goalkeeper Gavin Bazunu and Greg Bolger slotting into midfield.
The visitors had the first big chance of the game after the Blues failed to clear Ronan Finn's inswinging free kick but Roberto Lopes, a late inclusion for Joey O'Brien, couldn't flick the ball in with the goal at his mercy. Minutes later a fantastic covering tackle from Rory Feely prevented Dan Carr from pulling the trigger while Izzy Akinade couldn't hit the target after a weak defensive header fell to him on the edge of the box at the other end.
The majority of the 2,378 fans in the stands were calling for a penalty mid-way through the half after Duffus was felled by Brandon Kavanagh but referee Robert Harvey waved away the Blues appeal.
An outstanding double save from Waterford's netminder Matthew Connor kept the game level on the half hour mark. Aborah missed the chance to clear a Kavanagh corner allowing Dylan Watts to nip in and drive an effort goalwards before Finn's volleyed rebound produced an even better save from Connor.
In injury time both sides had chances to grab an opener - Dylan Barnett's effort after an Akinade cross flew narrowly wide of Mannus' left post while early substitute Sam Bone glanced a header wide before the half concluded.
Rovers started the brighter side after the restart although Connor was never tested, while Paul Keegan's floated corner finding Feely in the box on the hour mark, although his header looped over the goal.
Hery had an effort saved by Mannus and the Northern Irish keeper again kept his side level with a stunning double save. Former international Noel Hunt played in Holohan who's low-effort was tipped away by Mannus, who jumped up to prevent Akinade's follow-up from crossing the line.
The deciding goal arrived in the 74th minute when Shaw dived to head in Bone's tempting delivery from the right wing and Joel Coustrain could have doubled the lead shortly afterwards after some good link-up play between Watts and the goalscorer.
The home side pushed for a crucial equaliser, with a 78th minute shot from Akinade clipping the outside of the post, but Stephen Bradley's side held on to become just the second side to beat the Blues at home this season.
Waterford FC: Matthew Connor; Rory Feely, Kenny Browne, Dave Webster, Dylan Barnett; Paul Keegan (C); Stanley Aborah (Puri, 84), Bastien Hery; Gavan Holohan (Hutchinson, 81); Courtney Duffus (Hunt, 64), Ismahil Akinade.
Substitutes: Niall Corbett (GK), Garry Comerford, Noe Baba, Sander Puri, Noel Hunt, Dean O'Halloran, Dessie Hutchinson.
Shamrock Rovers: Alan Mannus, Ethan Boyle (Bone, 12), Roberto Lopes, Lee Grace, Luke Byrne; Greg Bolger, Dylan Watts; Joel Coustrain, Ronan Finn, Brandon Kavanagh (Greene, 61); Dan Carr (Shaw, 61).
Substitutes: Kevin Horgan (GK), Joey O'Brien, Gary Shaw, David McAllister, Aaron Bolger, Aaron Greene, Sam Bone.
Referee: Robert Harvey
