Ospreys 18 (10)
Tries: S Williams, R Jones, R Pugh.
Pens: G Henson.
Blues 16 (13)
Tries: N Robinson.
Cons: N Robinson.
Pens: N Robinson.
DG: N Robinson 2.
Ritchie Pugh snatched victory for the Ospreys in a fierce match against rivals Cardiff Blues on Wednesday.
Blues fly-half Nick Robinson, who scored all 16 of his side's points, looked to have snatched it with his second drop-goal of the night.
But it was his loose kick as time ran out that allowed replacement flanker Pugh to race over and claim the win.
The Blues' misery was compounded as back-row Robin Sowden-Taylor suffered a badly broken ankle in the last minutes.
Ospreys started at pace as Shane Williams crossed the whitewash within five minutes.
The Wales wing took a quick line-out to Lee Byrne and when the full-back was stopped by three tacklers, Williams was on hand to race clear up the right touchline.
Gavin Henson missed the difficult touch-line conversion, but opposite fly-half Robinson got the Blues on the score-sheet with a penalty.
Robinson then claimed a try, starting the move with a chip that was fielded by Mosese Luveitasau.
The fly-half took a return pass from the Fiji wing to go under the posts, Robinson converting the try himself.
Although trailing, the Ospreys kept their composure with Henson and Justin Marshall kicking to the corners to keep the Blues pinned back.
That reaped dividends when the home side earned a five-metre scrum and Ryan Jones drove off the base to score an unconverted try that levelled the scores.
The Blues still managed to get their noses back in front before half-time, as Robinson clipped over a drop-goal to claim a 'full-house' of scoring.
After the restart both sides wasted great opportunities by losing the ball forward at the vital moment, while Byrne just failed to touch down Marshall's grubber-kick.
A Henson penalty brought the Ospreys level once more as the match entered its final 15 minutes.
The attritional nature of the game was taking its toll, with the physios from both sides kept busy.
The Blues front-row had been hit particularly hard and scrums had to be uncontested for the remainder of the match.
With defences on top it was likely that a kick would decide such a tight affair and Robinson pumped over a 40-metre drop-goal.
But the Blues fly-half blotted his immaculate display with a clearing kick that went straight up in the air.
Ospreys replacement open-side Pugh plucked the loose ball out of the air and raced over for a dramatic winning try.
Ospreys: Lee Byrne; Nicky Walker, Sonny Parker, Andrew Bishop, Shane Williams; Gavin Henson, Justin Marshall; Duncan Jones (capt), Huw Bennett, Adam Jones, Brent Cockbain, Ian Evans, Andy Lloyd, Jonathan Thomas, Ryan Jones.
Replacements: Richard Hibbard, Paul James for Adam Jones (75), Lyndon Bateman for Evans (80), Alun Wyn Jones for Cockbain (47), Richard Pugh for Lloyd (57), James Hook, Stefan Terblanche for Byrne (77).
Blues: Rhys Williams; Chris Czekaj, Tom Shanklin, Marc Stcherbina, Mosese Luveitasau; Nick Robinson, Mike Phillips; Gethin Jenkins, T Rhys Thomas, Tufaao Filise, Deiniol Jones, Rob Sidoli, Scott Morgan, Martyn Williams, Xavier Rush (capt).
Replacements: Gary Powell for Goodfield (68), Duane Goodfield for Thomas (29), Bradley Davies, Robin Sowden-Taylor for M. Williams (77), Wayne Evans for Sowden-Taylor (80), Nick Macleod for R. Williams (68), Tom Riley.
Referee: Nigel Owens (WRU).
Att: 10,020