Cardiff Blues survived an onslaught from Pau's powerful pack to book a place in the European Challenge Cup final.
The Blues will face Gloucester at Bilbao's San Mames Stadium on May 11 following a pulsating Arms Park clash that went their way 16-10.
The home side emerged victorious despite Pau enjoying sustained scrum dominance that saw them gain several penalties from referee John Lacey.
But the Blues, Challenge Cup winners in 2010, held their nerve as full-back Gareth Anscombe scored an early try, while Wales fly-half hopeful Jarrod Evans kicked three penalties and a conversion.
Pau's World Cup-winning former New Zealand centre Conrad Smith touched down for the visitors, with fly-half Tom Taylor adding a conversion and penalty, but the French side ultimately suffered their first defeat in this season's competition.
They had breezed through the pool phase by collecting 29 points from a possible 30, yet the Blues proved tough nuts to crack as young talents like Evans, lock Seb Davies and flanker Ellis Jenkins all delivered performances of impressive maturity.
And the Welsh challengers dug deep during an intense second period that produced just three points before claiming a showdown in Spain against Gloucester.
The Blues made a flying start as they breached Pau's defence inside six minutes.
Evans was the catalyst, rifling out a defence-splitting pass to lock Davies, who then timed his delivery perfectly to an unmarked Anscombe and the Blues were off and running.
Evans converted from the touchline and Pau - despite some early impressions in the loose by their juggernaut forwards - found themselves seven points adrift.
The setback, though, did not deter them in terms of applying relentless scrum pressure, and after Taylor missed a 17th-minute penalty, they drew level by capitalising on an Anscombe error.
The Wales international's attempted clearance from just outside his 22 was charged down by Pau lock Julien Pierre, and although Pierre could not gather, Smith kicked on and won the race to claim a try that Taylor converted.
Evans then kicked a penalty to edge the Blues back in front, and although Taylor landed an equalising strike, Evans came up trumps again two minutes before half-time as his team shaded a fierce first half 13-10.
Pau captain Thibault Daubagna missed with a long-range penalty attempt early in the second period and Pau - marshalled superbly by their midfield general Smith - began to show some attacking prowess.
But the visitors could not make it count in the Blues' 22, and Evans made them pay when he kicked a 40-metre penalty six minutes from time and sparked celebrations for an 11,700 crowd.