Parker showed he was back to form with a fine opening try
Blues: (3) 10
Ospreys: (10) 27
Tries: Parker, Byrne
Pens: Hook (4)
The Ospreys eased into the EDF Energy Cup final with a comfortable win over the indisciplined Cardiff Blues.
Having denied that this was a grudge match, the Blues lost their head with three first-half sin-bins.
James Hook profited from the penalties with 17 points, with Sonny Parker and Lee Byrne crossing for tries when the opposition were down to 14 men.
Ben Blair got a late consolation try, but could not stop the Ospreys making the 15 April final against Leicester.
The Tigers had earlier battled to Twickenham with a hard-fought 29-19 win over Sale Sharks in the first game of the semi-final double-header in front of 40,293 at Cardiff's Millennium Stadium.
I offered to shake hands at the end but it wasn't taken - he's young and maybe he'll get more mature in the future
Justin Marshall on Mike Phillips
Although both sides had spent the build-up week denying it, the rivalry between the two Welsh sides was obvious.
That followed two fiery league encounters between them this season, where honours were shared.
Blues scrum-half Mike Phillips' anticipated big-money summer move to the Ospreys fuelled the feud, and it was predictably his motivated opposite number Justin Marshall who claimed the man-of-the-match award.
Hook and Blair unusually missed straightforward penalties in the early exchanges, before Blues full-back Blair got the scoreboard ticking with a 12th-minute penalty.
The first indiscretion from the Cardiff side soon followed, though, Scott Morgan coming in at the side of a ruck - and being punished with a yellow card and a penalty from Hook.
Hook showed his composure and class once more
With the Blues down to 14 men, Parker put in a neat step in midfield to break the tackle of Wales centre rival Jamie Robinson.
The Kiwi still had plenty to do, but showed the pace and power to cross in the corner for a try, beautifully converted by Hook.
From the restart, Blues lock Deiniol Jones clumsily took Alun Wyn Jones out in the air, meaning that he joined Morgan in the sin bin.
Morgan returned, but moments before half-time his side was back to 13 men when Robert Sidoli raised his hand at Brent Cockbain and pushed his opposite number to the floor.
Deiniol Jones was back in the action at the start of the second half, but a delightful pass from Hook helped create space out wide for Byrne.
The Wales full-back cut through some weak midfield tackling to score an unconverted try in the corner.
The Blues fought back, but lacked a clinical edge and when Chris Czekaj crossed his try was ruled out for crossing.
Hook added three more penalties, but the Ospreys went to sleep from the third restart, misjudging the kick that fell to the Blues.
They launched a sweeping attack, Nicky Robinson's wide pass finally beating the rush defence and sending Blair over in the corner for a try that the Kiwi converted superbly.
That brought the Blues back to within two scores, but from the next Ospreys attack Hook showed the awareness to stretch out the lead with a well-taken drop-goal.
But the controversy was not even over after the final whistle as Marshall offered a handshake in the tunnel to Phillips, and received a shoulder charge in return.
Man-of-the-match Justin Marshall:
"We got a bit of a pasting the last time we played the Blues, but this time we were very efficient and got the job done.
"We felt we were a bit unlucky to miss out on the Heineken Cup this year, but now hopefully we can win something - we haven't done it yet, but we'll look forward to Twickenham.
"Mike Phillips' presence played no part in my performance, it was for the team.
"I'm well settled in Swansea and I'm going nowhere so we'll be team-mates next year.
"There was a bit of an altercation at the end - that was about mirror space!
"I offered to shake hands but it wasn't taken. He's young and maybe he'll get more mature in the future."
Ospreys: Byrne, S. Williams, Parker, A. Bishop, Walker, Hook, Marshall, D. Jones, Bennett, A. Jones, Cockbain, A. Jones, R. Jones, Thomas, Tiatia.
Replacements: Terblanche for Byrne (76), Connor for Hook (76), Spice for Marshall (76), B. Williams for Bennett (74), James for A. Jones (76), Pugh for Tiatia (73). Not Used: Lloyd.
Cardiff Blues: Blair, James, J. Robinson, Stcherbina, Czekaj, N. Robinson, Phillips, Filise, Thomas, G. Powell, Jones, Sidoli, Morgan, M. Williams, Rush.
Replacements: Macleod for J. Robinson (74), Roberts for Filise (76), G. Williams for Thomas (72), Davies for Jones (58), Lewis for Morgan (70). Not Used: Evans, Luveitasau.
Referee: Wayne Barnes (England).