Tries: Thornton, Belcher, D Thomas Cons: Sheedy 3 Pens: Sheedy
Cardiff improved their United Rugby Championship (URC) play-off hopes with victory in a compelling Welsh derby against Ospreys at the Arms Park.
The victory lifted the Blue and Blacks to fourth in the table with their play-off rivals all playing on Saturday as the rivals battle to finish in the top eight.
Cardiff scored tries through lock Rory Thornton, captain Liam Belcher and flanker Dan Thomas while Callum Sheedy kicked nine points.
Ospreys wing Daniel Kasende was shown a 20-minute red card in the first half for dangerous play.
There were further yellow cards for centre Owen Watkin and fly-half Dan Edwards as Ospreys played almost half the game with fewer than 15 players on the field.
Cardiff duo Belcher and lock McNally were also shown yellow cards in a match that was rarely 15 against 15.
Ospreys centre Keiran Williams scored a first-half try, while late scores from full-back Jack Walsh and Edwards set up a dramatic finale, but Cardiff clung on.
It was Cardiff's first win against Ospreys at the Arms Park since 2007 and played in front of 12,036 fans with Welsh Rugby Union (WRU) chief executive Abi Tierney in the crowd.
The home side have also gone five points clear in the battle for the Welsh Shield.
This is a sub-competition within the league which acts as a domestic championship to determine local bragging rights.
It is separate from the main URC league table and the winner is decided by head-to-head matches, not league positions, during the regular season.
Ospreys face Scarlets on Saturday, 9 May in Bridgend and will need a significant bonus-point win to usurp current holders Cardiff.
There had been drama this week concerning the two sides when the WRU announced its controversial plan of selling Cardiff to Ospreys owners, Y11 Sport & Media, had fallen through.
That happened just 48 hours before the two sides face each other in a crucial league game so this fixture could no longer be coined the "Y11 derby".
There was enough at stake on the field after Cardiff's remarkable comeback win against the Scarlets had kept Corniel van Zyl's side in the top half of the table.
Cardiff were missing injured Wales internationals Josh Adams, James Botham, Taulupe Faletau and Mason Grady, with Wales Under-20s wing Tom Bowen named among five changes.
Wales prop Gareth Thomas had initially been passed fit to start for Ospreys after passing a head injury assessment with fellow loose-head Garyn Phillips ruled out.
Thomas was ruled out before kick-off and replaced by his cousin and namesake Steffan.
Ospreys also named wing Luke Morgan who suffered online abuse after his challenge on Sharks' Ethan Hooker in the 21-17 win in Bridgend.