Newport Gwent Dragons dented Cardiff Blues' Magners League play-off hopes with a thrilling Rodney Parade win.
The defeat leaves the door ajar for both the Scarlets, who host the Blues in next week's final round, and the Ospreys who travel to Aironi.
Steffan Jones' opening try and his late long-range penalty helped deny the Blues a losing bonus point, with Aled Brew and Andrew Coombs also crossing.
Sam Warburton and Xavier Rush grabbed Blues tries either side of half-time.
The result sets up a mouth-watering final round of matches next Friday, with the Blues' live televised trip to Parc y Scarlets now of massive significance.
The Blues must win to ensure a place in the play-offs, while the Scarlets can leap-frog their Welsh regional rivals with a win - providing the Blues do not claim a bonus point for either losing by seven points or fewer, or scoring four tries.
If the Scarlets do win then they must hope that the Ospreys slip to defeat out in Italy the same evening against bottom club Aironi.
The Dragons are out of the race to make the play-offs themselves, and have already missed out on a Heineken Cup place, but could still have a huge say in who makes the Magners League knock-out stage.
Ulster, currently in third place, must travel to Rodney Parade in their final match knowing that defeat could allow both the Blues and Ospreys to overhaul them, although a bonus point will be enough to keep the Ospreys at arm's length.
The Blues wanted to wrap things up in Newport and led through an early Dan Parks penalty.
But the Dragons were soon on the front foot thanks to a brilliant try on debut from teenager Jones.
The full-back had been drafted in from Cross Keys to cover the Dragons' injury crisis but after just seven minutes burst through a gap in the Blues' defence.
Picking a fine line between full-back Dan Fish and lock Bradley Davies, Jones shaped as if to pass but stepped on the gas to dive over in the corner, with Jason Tovey converting.
Dragons wing Aled Brew soon followed Jones to the line after a cross-kick from stand-off Tovey was tapped down by lock Luke Charteris into the Wales international's hands for an easy run-in.
Tovey missed that conversion but made amends soon after with a penalty to extend the Dragons' lead further.
But when home lock Adam Jones was sent to the sin-bin for preventing the ball from coming out of a ruck on his line the Blues got back into the match.
Flanker Warburton immediately grabbed a try from a pick-up and drive by Rush from the base of an attacking scrum.
Parks' conversion trimmed the Dragons' lead to 15-10 at half-time and the Blues levelled six minutes after the restart, when a five metre line-out saw the Blues pack drive Rush over the line.
But fierce Dragons defence kept the Blues from crossing the line despite a series of attacks deep into the home 22.
The Dragons retook the lead when a line-out within metres of the Blues' line saw Charteris take the throw and he helped his pack drive replacement back-rower Coombs over for a converted try.
That made it 22-15 but Steffan Jones' booming 50-metre penalty a minute from time gave the Dragons a 10-point gap - and took away a crucial losing bonus point from the Blues.
Dragons scrum-half Wayne Evans rubbed in an impressive victory with a drop-goal from 10 metres right at the death.
NG Dragons: Steffan Jones; Adam Hughes, Tom Riley, Ashley Smith, Aled Brew; Jason Tovey, Wayne Evans; Phil Price, Lloyd Burns, Ben Castle, Luke Charteris (capt), Adam Jones, Dan Lydiate, Gavin Thomas, Toby Faletau.
Replacements: Tom Willis for Castle (62), Hugh Gustafson for Price (70), Dan Way, Andrew Coombs for A. Jones (62), Lewis Evans for G. Thomas (49), Pat Leach for Hughes (41), Jonathan Evans, Matthew Jones.
Cardiff Blues: Dan Fish; Chris Czekaj, Casey Laulala, Jamie Roberts, Tom James; Dan Parks, Richie Rees; John Yapp, Gareth Williams, Taufa'ao Filise, Bradley Davies, Paul Tito (capt), Michael Paterson, Sam Warburton, Xavier Rush.
Replacements: Rhys Williams, Sam Hobbs for Yapp (23), Scott Andrews, Deiniol Jones for B. Davies (43), Ma'ama Molitika, Lloyd Williams, Ceri Sweeney for Parks (60), Dafydd Hewitt for Laulala (41).
Referee: James Jones (WRU).