Tries from Lee Byrne and Filo Tiatia helped the Ospreys overcome the Cardiff Blues in a tense New Year’s Eve derby clash at the Arms Park, with the result sending Sean Holley’s side to the top of the Magners League.

Five minutes from time, Ospreys number 8 Tiatia fended off a tackle from Richard Mustoe and crossed in the left corner for what proved to be the match-winning try.

Cardiff launched a late fightback, with Tom Shanklin helping the home side march their way back into the Ospreys’ 22, but they could not conjure up a try in reply and the former champions, who trailed 9-8 at half-time, held on to complete their first win away to a fellow Welsh region since May 2007.

The Blues welcomed back Wales and Lions duo Martyn Williams and Gethin Jenkins into their starting line-up and were looking to follow up on their 21-19 win over the Newport Gwent Dragons on Boxing Day.

Both teams came into this game on the back of three wins in their last four outings in all competitions and Cardiff had some extra motivation as they remembered their 32-10 defeat at the Ospreys in September.

The Ospreys travelled with a rejigged team – most notably regular full-back Lee Byrne was switched to the wing to cover for the injured Shane Williams and Gavin Henson reverted to number 15.

Impressive youngster Dan Biggar got the nod to start at number 10, partnering Mike Phillips who was starting his second game since returning from a long term cruciate ligament injury.

This is arguably the biggest rivalry in Welsh domestic rugby and the tension was obvious during the early stages.

With no quarter given, predictably it was a stop-start opening and referee Nigel Owens, whistling his 50th league game, had a busy time of it.

The returning Jenkins took the ball into contact, drew a penalty and Ben Blair stepped up to slot between the posts to give the Blues a second minute lead.

Biggar quickly levelled though, after a high tackle from Taufa’ao Filise, but both place-kickers showed signs of nerves when they missed their next shots at the posts.

Warming to their task in the cold conditions, the hosts began to find space with both Shanklin and Williams beating first-up tackles and when Marty Holah was penalised for killing the ball in the 13th minute, his fellow New Zealander Blair made it 6-3 to Cardiff.

Blair’s afternoon was soon cut short by injury, with Wales international Leigh Halfpenny coming on in his place.

Helped by a solid set piece platform, the Ospreys enjoyed a purple patch coming up to the midpoint of the first half.

Centre Sonny Parker’s rampaging run down the left preceded a decent spell of territory for the visitors and they really should have poached their first try from it.

Holah sent an ill-advised grubber kick through when he should have perhaps kept the ball in hand and Biggar also erred when he sent out a looping pass which hampered the supporting Henson and Cardiff won a relieving penalty.

But tempers flared when Blues captain Paul Tito and Ospreys hooker Richard Hibbard had an off-the-ball scuffle which the match officials did well to diffuse.

With minds back on the rugby, the Ospreys broke through for their opening try eight minutes before half-time.

It all started with a brilliant bit of ball-juggling from Biggar, who showed his agility to rescue possession when a knock-on seemed certain.

Tommy Bowe then made serious yards down the left wing, with the Cardiff defenders backing off, and he passed out of the tackle to the supporting Byrne who was able to step inside Ma’ama Molitika and make the corner just ahead of Tom James.

Biggar missed the conversion and Cardiff almost responded with a ‘wonder’ try three minutes later.

Halfpenny made a sumblime break, collecting a clearance kick by Biggar and accelerating past three would-be tacklers.

Henson eventually hauled the Cardiff replacement down just short of the try-line and also managed to rip the ball back on the Ospreys side, allowing Bowe to get a kick away to touch.

But the Blues at least came away from that visit to the visitors’ 22 with points as a drop goal from fly-half Nicky Robinson saw them wrestle back the lead (9-8) for the interval.

Both Biggar and Robinson, who was kicking in Blair’s absence, missed penalty kicks at the start of the second half and the game seemed to turn in Cardiff’s favour on the hour mark.

A trademark surging run from winger James saw him take play from his own 22 into the Ospreys’ one and it took a well-timed cover tackle from Byrne to stop him from scoring.

But as Byrne tried to defend at the ensuing ruck, he was whistled up for coming in at the side and referee Owens produced a yellow card – much to the Ospreys’ dismay.

Robinson kicked the resulting left-sided penalty for a 12-8 Cardiff lead but Dai Young’s charges could not make use of their one-man advantage and indeed the Ospreys quickly cancelled out that score with a long range penalty from replacement James Hook.

Hook proved to be an inspired inclusion for the final quarter as he helped the Ospreys mount a series of attacks which ultimately resulted in Tiatia’s decisive try.

With the Ospreys forwards getting up a head of steam, Cardiff were loosing chunks of territory and it took strong defence, particularly from Halfpenny who put in two last-ditch tackles, to maintain the Blues’ slim advantage.

But all that disciplined defending was undone in the 75th minute when Tiatia scored from close range.

A quick change of direction from Jamie Nutbrown and Hook split open the Cardiff defence and the latter spun a lovely pass out for the waiting Tiatia to crash past Mustoe and muscle his way across the line.

Hook’s conversion attempt spun the wrong side of the right post but it did not matter in the end as despite enjoying the lion’s share of possession for the remaining eight minutes, Cardiff were unable to make it count as the Ospreys vaulted over Munster at the top of the standings.