Cardiff took a giant step towards the URC play-offs as they secured a thrilling Welsh derby victory to move up to fourth in the table.

There were tries for Rory Thornton, Liam Belcher and Player of the Match Dan Thomas on an eventful evening when four yellow cards and one red were handed out.

The Ospreys staged a late rally to set up a grandstand finish, but Cardiff held on to the delight of their supporters in a 12,036 crowd at a packed Arms Park.

It’s a win which takes them up to 50 points with two regular season games left to play against Glasgow (a) and the Stormers (h).

There is still work to do, depending on results elsewhere, but they are now within touching distance of making history by reaching the play-offs for the first time.

This was a victory which was all the more creditable as they went into the game without 11 first team players through injury.

Following on from last weekend’s dramatic comeback victory against the Scarlets, Cardiff had made five changes in personnel and one positional switch.

There was a promotion to the starting line-up for tighthead prop Javan Sebastian after his super-sub try double against his former team down in Llanelli, while Thornton got the nod at lock.

Then in the back row, Taine Basham and Dan Thomas came in at No 8 and openside respectively with James Botham ruled out by a HIA. That meant a move across to the blindside flank for Alun Lawrence who leads the way for both carries and tackles in the URC this season.

The solitary alteration behind the scrum saw Tom Bowen step in on the wing for Mason Grady who fractured his thumb in the 28-24 bonus point win over the Scarlets.

There was a late change among the replacements with centre Elijah Evans taking over from Alex Mann which meant a 5-3 split on the bench as opposed to the originally planned 6-2.

The Ospreys also made an eleventh hour switch, with prop Gareth Thomas withdrawing and his berth on the loosehead being filled by his cousin Steffan Thomas.

It proved to be a hugely eventful first half which only saw eight minutes of 15-a-side rugby amid a flurry of cards of varying colour.

Cardiff were the first team to be reduced in number with hooker Belcher yellow carded for head-on-head contact in attempting to tackle Morgan Morris.

But, as it turned out, they scored the only points during the sin bin period with Callum Sheedy slotting a kick just before his skipper’s return.

That penalty was awarded against Dan Kasende for leading with his forearm into Sheedy’s face and a TMO review saw the South African winger issued a yellow card. As it turned out, that wasn’t to be the end of the matter.

First though, Cardiff capitalised on their extra man as Thornton forced his way with an accompanying shove from Belcher after scrum-half Johan Mulder had taken a quick tap penalty.

That also saw Owen Watkin sin binned for an offence near his line and things were to get even worse for the Ospreys after Sheedy’s conversion with South African referee Christopher Allison announcing that Kasende’s card had been upgraded to a 20 minute red card on review.

To their credit, the visitors held out despite being down to 13 men and once restored to 14 by Watkin’s return they struck with a try of their own three minutes before the break.

It looked as though they had spurned the attacking opportunity when an overthrow saw the ball sail over the top of a lineout.

But fly-half Dan Edwards pounced on the bouncing loose ball and cut through before sending centre Keiran Williams over for a converted try.

That reduced the deficit to 10-7 at the end of a first half which certainly wasn’t short on incident.

Within five minutes of the resumption, yet another yellow card was issued as Ospreys No 10 Edwards was guilty of a deliberate knock-on.

The hosts capitalised immediately with Belcher taking a tap penalty and reaching the line himself with the help of a couple of his forward pals.

Then, just before Edwards’ return, they struck again with a score which owed much to two key contributions from centre Rory Jennings.

First he put in a crucial clear-out to retain possession after Jacob Beetham had collected Ben Thomas’ cross kick and he then carried strongly up to the whitewash ahead of Dan Thomas adding the close range finish.

Sheedy duly landed his third successful conversion to make it 24-7 as the game moved into the final quarter.

The Ospreys then cut the deficit with a converted try of their own when replacement prop Cam Jones burst through from halfway and gave an inside scoring pass to full-back Jack Walsh who managed to get the ball down despite colliding with a post.

Yet another yellow card was handed out six minutes from time when Cardiff lock Josh McNally was binned and the Ospreys swiftly took advantage with Edwards diving in from close range and slotting the conversion.

But Cardiff saw the game out in the dying minutes to secure a priceless win.