Late tries from Ryan Jones and Hanno Dirksen saw the form book turned on its head as RaboDirect Pro12 league leaders Scarlets went down 23-16 at home in a tense Welsh derby to the previously winless Ospreys.
The score was locked at 9-9 until the Ospreys came up with their tries in the space of three minutes. Dan Biggar supplied 13 points with the boot.
Wales wing George North grabbed a late try to seal a losing bonus point for Scarlets, with Rhys Priestland kicking 11 points, but he missed four penalty attempts as well.
The Scarlets approached the game as league leaders with three straight wins, and in contrast the Ospreys were second from bottom after losing all three of their matches. But the Ospreys, lifted by the intensity of a derby, were far more competitive.
The Scarlets had a try disallowed by the television match official after wing Andy Fenby failed to ground the ball, although he seemed to be high-tackled by George Stowers as he went over the line.
Biggar missed a penalty after 26 minutes but found the target eight minutes later as the Ospreys led for the first time, and the visitors went to half-time with a 9-6 advantage.
The Ospreys thought they had scored a try three minutes after the break through Dirksen but it was disallowed for a forward pass. And as the Scarlets worked their way upfield they levelled the scores at 9-9 after 47 minutes with a third Priestland penalty.
The Ospreys brought on Ryan Jones for his first appearance of the season just as Priestland missed a chance to take his side into the lead. And the Scarlets suffered a blow on the hour mark when their replacement prop Samson Lee was yellow-carded following a collapsed scrum.
Back to 15 men, the Scarlets conceded the key try after 72 minutes when Ryan Jones finished off a forward drive from a lineout. The Biggar conversion put the Ospreys 16-9 ahead.
And three minutes later Dirksen was in at the right corner for the second Ospreys try, with Biggar again adding the extras. The game was effectively gone for the hosts, but small consolation arrived with seconds on the clock as North went over to earn the bonus point and Priestland booted the conversion.