Determined to go out with their heads high before being disbanded, the rock bottom Scottish outfit gave the Ospreys a major scare before they clinched the title at Netherdale.
After Sonny Parker had added his second try to Filo Tiatia's fifth minute opener, the champagne was being put on ice, but the Borders, with Calum MacRae's boot to the fore, launched a late fightback through replacement prop Ed Kalman's try. MacRae's conversion and penalty moments later brought Borders within five points.
With the pressure mounting against them the Ospreys were suddenly awarded a penalty deep into injury time. James Hook, who bagged nine points in all, stepped up with composure and sealed the title for the Ospreys.
Cardiff Blues had seized temporary control of the Championship following their Friday night win over Leinster; leaving the Ospreys needing just a win against a Borders side playing their last ever game. It took the Ospreys just five minutes to settle any nerves with their opening try as Tiatia went through a gaping hole in the Scottish defence to go under the posts handing Hook an easy conversion.
A penalty from Calum MacRae soon after got the Reivers moving on the scoreboard, but the Ospreys were always in control and grabbed their second try after Hook sent Parker over for another seven points. MacRae reduced the deficit to 14-6 at the break.
The Ospreys ran out for the second half with the seven point cushion behind them and the title within their grasp. It was all but sealed when Shane Williams and the impressive Hook combined to free Parker to slide in at the left corner, with Hook adding the extras. However, if the Ospreys thought the job was done they were soon given a wake-up call; the Borders were determined not to go out with a whimper.
Gregor Townsend, in his last game before retirement, sparked a move that saw replacement prop Kalman burrow over. MacRae added the touchline conversion and then a penalty from in front of the posts to cut the Ospreys' lead to just five points with ten minutes remaining.
Richie Pugh had a golden chance to settle Welsh nerves after breaking clear down the left wing but his pass to Lee Byrne went to ground. As ever, the ice cool Hook typically had the last say as his long range penalty saw the Welsh region edge over the finishing line to claim their second Celtic crown in three seasons.
Border Reivers 16 (6)
Pens: MacRae 3
Ospreys 24 (14)
Tries: Tiatia, Parker 2
Cons: Hook 3