Cardiff Blues: (27) 30
Ben Blair dives over for his second try for the Blues
Tries: N Robinson, Blair (2)
Cons: Blair (3)
Pens: Blair (3)
Ospreys: (9) 24
Tries: Tiatia, Evans
Pens: Henson (4)
Cardiff Blues survived a brave Ospreys fightback to win an enthralling Magners League encounter at the Arms Park.
Tries from Nick Robinson and Ben Blair (two), who finished the match with a personal points tally of 25, gave the Blues a 27-9 lead at the interval.
The Ospreys were a different side after the break and hit back with tries from Filo Tiatia and Ian Evans.
But the Blues held on in the final stages despite having Martyn Williams sent off a Mike Phillips yellow carded.
Powell was penalised for a spear tackle and then Williams followed him off after a headbutt on Jason Spice in the resulting fracas.
The Blues tries in the first-half arrived during a 15-minute purple patch which gave the home side a stranglehold on the match.
Fly-half Robinson got the ball rolling on seven minutes when he intercepted Justin Marshall's long pass on the halfway line and had enough pace to touchdown.
Blair, moved to the wing from his usual full-back position, crossed three minutes later after taking Jamie Robinson's well-timed off-load in the tackle a few yards short of the tryline.
The Kiwi had far more ground to cover for his second try as he gathered Shane Williams' attempted kick inside his own half and raced down the right win to score in the corner.
All three tries were converted by Blair, adding to his fourth-minute penalty.
Ospreys looked disjointed in attack as Henson, who kept his side in touch with three penalties, struggled to orchestrate matters at fly-half.
The visitors did cross the Blues tryline in the final minute before the break, but number eight Tiatia was denied after the referee had spotted a forward pass.
A few harsh words from coach Lyn Jones seemed to work wanders as the Ospreys came out firing after the interval.
A sustained period of pressure inside the first 10 minutes finally told as Tiatia barged through Gary Powell's attempted tackle to score in the right corner.
Henson landed a superb conversion and a remarkable comeback looked a distinct possibility when lock Ian Evans finished off a flowing move to close the gap to 27-21 with just under 20 minutes remaining.
Blair and Henson then landed a penalty apiece, and despite losing two players in the closing stages, the Blues managed to repel the Ospreys' frantic last attacks to claim victory.
Cardiff Blues captain Xavier Rush:
"We had a good first-half but the Ospreys came back pretty hard in the second-half where we took our foot off the pedal a little bit.
"It was a bit unfortunate thee match ended like it did because it had been such a good game up until that point.
"But tempers flare in those sort of circumstances when the pressure comes on and it obviously was too much for a couple of the guys."
Ospreys coach Lyn Jones:
"We're disappointed with the result and I believe the Blues were fortunate to score the points they needed in the first-half.
"We played much better in the second-half and we were a little unfortunate not to win the game.
"But when you give the Blues a lead like we did, it's difficult to come back."
Cardiff Blues: Nick Macleod, Ben Blair, Jamie Robinson, Tom Shanklin, Chris Czekaj; Nick Robinson, Mike Phillips; Gethin Jenkins, T Rhys Thomas, Gary Powell, Bradley Davies, Deiniol Jones, Scott Morgan, Martyn Williams, Xavier Rush (capt).
Replacements: Taufaao Filise for Powell (67), Ben White for Davies (75). Not Used: Gareth Williams, Rhys Shellard, Ed Fairhurst, Dai Flannagan, Dafydd Hewitt.
Sin bin: Phillips (80)
Sent off: Williams (80)
Ospreys: Stefan Terblanche; Nikki Walker, Sonny Parker, Andrew Bishop, Shane Williams; Gavin Henson, Justin Marshall; Duncan Jones (capt), Barry Williams, Adam Jones, Brent Cockbain, Ian Evans, Alun Wyn Jones, Ryan Jones, Filo Tiatia.
Replacements: Jason Spice for Marshall (40), Lee Byrne for Terblanche (51), Ritchie Pugh for Cockbain (57), James Hook for Parker (62), Cai Griffiths for A. Jones (70). Not Used: Ed Shervington, Andy Lloyd.
Referee: Tim Hayes (WRFU)