Halfpenny celebrates after scoring the Blues' first try
Cardiff Blues will play Toulon in Marseille in the Amlin Challenge Cup final on 23 May after battling to a tense semi-final win over London Wasps.
The Welsh region out-scored their hosts two tries-to-nil, wing Leigh Halfpenny and prop Gethin Jenkins both crossing.
Dave Walder landed five penalties for the English side, three in the first half to help the hosts to a 9-8 lead.
But the Blues moved 18-12 up after Jenkins' try and Walder missed a late kick that would have meant extra-time.
While that was harsh on the fly-half who had been immaculate with the boot until that point, the Blues deserved victory if only for the outstanding individual display of captain Xavier Rush.
The number eight carried the ball on 24 occasions, taking the fight to Wasps in wet conditions after a deluge in the two hours before kick-off at Adams Park.
It was a day for rolling up your sleeves and showing plenty of guts
Blues captain Xavier Rush
The hosts, unbeaten in their last 16 European matches at home, edged the opening 40 minutes largely thanks to a better kicking game and strong scrummage.
The Blues started brightly and looked more dangerous with ball in hand, Rush bursting through before offloading to Ben Blair, who knocked on near the line.
The Kiwi full-back was narrowly off target with his first penalty attempt in the seventh minute, a trend that briefly threatened to undermine the visitors' efforts.
He missed with two more attempts at goal, while Walder - selected ahead of Danny Cipriani, who only appeared for the final 10 minutes in his final home game before departing for Australia - slotted three penalties.
The Blues scored the opening try in the 28th minute after the inspirational Rush took a quick free-kick.
The New Zealander barged straight through Wasps scrum-half Joe Simpson and the ball was swiftly recycled to the right flank, where hooker Rhys Thomas slipped a smart pass to the lurking Halfpenny, who skipped inside Mark van Gisbergen to touch down.
Blair missed the conversion, but after Walder had kicked Wasps into a 9-5 lead, the Blues full-back found his range with his next penalty attempt to reduce the gap to a point at the interval.
Wasps, unbeaten in their last 16 European matches at home, went 12-8 ahead via Walder's fourth penalty on the resumption.
But Blair responded in kind after 53 minutes to keep the match finely poised.
I can't fault the effort but we were desperate to make the final. It is a pretty empty feeling
Wasps boss Tony Hanks
The visitors appeared to make a decisive move after veteran Wasps lock Simon Shaw was sent to the sin-bin in the 56th minute for his third infringement.
Halfpenny was narrowly off target with a penalty attempt from inside his own half before the Blues scored their second try, a series of pick-and-drives ending in Wales prop Gethin Jenkins plunging over.
Blair converted for an 18-12 lead heading into the final quarter, only for Walder to reduce the margin to three points with his fifth penalty before Shaw returned.
The Blues then found themselves a man short for the final 10 minutes when replacement Scott Andrews was sent to the sin-bin.
But they resisted manfully to reach a second final in successive seasons, after winning the Anglo-Welsh Cup last year.
Wasps, meanwhile, whose Premiership defeat by Bath last week means they are set to miss out on the play-offs, are left to ponder the likelihood of another trophy-less campaign.
Cardiff Blues number eight Xavier Rush:
"It was a game that guts was going to win it, not panache and fleshy stuff.
"We had to be quite patient as it didn't just come for us. I thought we played more of the rugby.
"Discipline and a few scrummaging issues cost us all of our points, but it wasn't looking like they would break us open or cut us to ribbons.
"We've made the final now so we will go down there and enjoy the occasion."
Wasps director of rugby Tony Hanks: "Credit to the Blues. We gave them a couple of soft penalties but they took their chances and a try count of 2-0 suggests they probably deserved to win. Their senior players really stepped up.
"I thought we were quite controlled and played smart in the first half. But we just didn't have enough of the ball and lacked field position to launch any meaningful attacks.
"I can't fault the effort. We wanted to respond after last week's defeat and we were desperate to make the final. It is a pretty empty feeling right now and we have got to make sure we learn from this.
"We have shown this season we can compete with the best, we just need to be a bit more consistent across the 80 minutes."
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