|Cardiff (12) 19|
|Tries: Lane, Belcher, Adams Cons: Evans 2|
|Ospreys (7) 22|
|Tries: Parry, Williams, Lake Cons: Williams 2 Pen: Williams|
The game was decided on the last kick of the game, as Evans missed the kick.
A 78th-minute penalty by Owen Williams proved to be the game winner.
Josh Adams' try appeared to have salvaged a draw for the hosts in the derby at Arms Park.
Indiscipline proved costly in the second half of the game.
Owen Lane and Liam Belcher scored for Cardiff in the first half as they took a 12-7 lead into the break.
The hookers scored identical driving lineout tries, either side of an opportunist score from Williams, as the visitors claimed a fifth successive win over Cardiff.
A sell-out crowd of 12,125 then held its breath after Jack Walsh was penalised in injury time, allowing Evans a final attempt to level for the second time from close to the touch line.
It is the third win in a row for the Ospreys.
The home crowd had been missing something when Liam took just five minutes to show them what they had been missing.
The full-back made the move that led to the game's opening try on his return after being injured.
Tomos Williams poked through a kick after winning a high ball. Walsh watched in horror as Lane was left with an easy first league try.
The early blow didn't deter the Ospreys from trying to get up front.
Their scrum, anchored by Tom Botha, had the edge, which allowed them to have a constant threat at number eight.
After their first meaningful lineout drive was rejected, a second saw Parry dive over on the back of their efforts. The fly-half fought through the rain to level the scores.
The pack hit back with a drive of their own within six minutes.
From the resulting penalty, Belcher barged over to regain the lead after his clever cross-field kick.
The full-blooded derby took its toll as both hookers were forced to leave within three minutes of each other.
The home team took a 12-7 lead at the break, but the visitors came back with two tries to take a 19-12 lead.
The scrum was their greatest weakness and they did well to defend it.
Owen Williams dived over for the try after Adam Beard tipped the ball that fell into his hands.
The television match official disagreed with the referee's decision to award the score.
Replacement hooker Lake scored from a lineout to give the visitors a 19-12) lead.
When Roots was shown a yellow card for his illegal tackle on Liam Williams, the game looked to have tipped in their favor.
It looked like it was going to be a close call, but it turned out to be the difference between victory and defeat.
Adams scored his seventh try in six games after Evans' cross-field kick sent him racing over, and Evans' conversion made it 19-19.
Williams missed a long range penalty but was given another chance after Myhill was sent to the sin bin for a high tackle.
Toby Booth is the head coach of the Welsh team.
The basics of rugby are taken over by set-piece and defence in conditions like that.
The boys did that and you have to do that as well. Rugby is a sport that involves physical contact. We dominated that area when we went through the front door.
It's great to back up a derby win. In tough games, it's about who can be the smartest.
Dai Young is the head coach of the Welsh team.
Losing is always disappointing. One of the Welsh regions was going to go down to the wire.
Penalties in the second half were a factor.
Our indiscipline and poor decisions around the breakdown gave them an easy field position. The lineout is going to convert a few of them if you give them five metres out.
Liam Williams; Owen Lane, Rey Lee-Lo, Ben Thomas, Josh Adams, Tomos Williams, Rhys Carre, Liam Belcher, Will Davies- King, Lopeti Timani, Seb Davies, Josh Turnbull, Thomas Young, Taulupe Fa.
Replacements: Kirby Myhill, James Ratti, Lloyd Williams, Teddy Williams.
Owen Williams, Tom Botha, Adam Beard, Alun Wyn Jones, Jac Morgan, and Justin Tipuric are the players who have been named in the squad.
Replacements: Dewi Lake, Tomas Francis, and Morgan Morris. Some of the people are: Joe Hawkins, Cai Evans.
The referee is Adam Jones from the Wru.
Ben Breakspear is an assistant referee.
The man is Wayne Davies.