Heymans and Medard had put Toulouse in complete control in the first half
Yannick Nyanga scored a dramatic last-minute, extra-time try as Toulouse held on for a thrilling Heineken Cup quarter-final win at Biarritz.
The defending champions had been 17-0 up at half-time courtesy of tries from Cedric Heymans and Maxime Medard.
But 17 unanswered points from Dimitri Yachvili and a 79th-minute Ilikena Bolakoro try levelled the scores.
Yachvili missed the last-gasp conversion before Nyanga slid over for the decisive score with seconds to go.
The substitute charged down Yachvili's clearance kick inside Biarritz's 22m line and the flanker collected the loose ball before touching down under the posts at the Estadio Anoeta in San Sebastian, the second Heineken Cup quarter-final to be held in Spain.
The four-time European champions will now travel to Dublin to play Leinster in the semi-finals.
Even without the invention of fly-half Frederic Michalak, scrum-half Byron Kelleher and flanker Thierry Dusautoir, Toulouse dominated the first half, scything through Biarritz's wafer-like defence on numerous occasions.
: Yachvili (5)
(17) Tries: Heymans, Medard, Nyanga,
: Skrela (2),
: Skrela (2), Bezy
Heymans superb footwork completely fooled Biarritz full-back Iain Balshaw, skipping over the tryline on 15 minutes before Medard collected a perfectly weighted crossfield kick from Nicolas Bezy 10 minutes later as the visitors took complete control.
Skrela added a penalty for a comfortable half-time lead - only to see the hosts respond with 17 unanswered points through the kicking accuracy of scrum-half Yachvili.
And the France international contributed to the score which tied the match in the final minute of normal time when he charged down Skrela's clumsy clearance kick inside Toulouse's 22m line, allowing Fijian winger Bolakoro to collect the loose ball and set up a potential match-winning conversion on the left touchline.
But Yachvili could not find enough direction to bisect the posts, prompting referee Wayne Barnes to whistle for extra time.
A Skrela penalty gave Toulouse a three-point advantage at the end of the first 10-minute half, but Yachvili's reliable left boot once again levelled matters with three minutes on the clock.
However, Yachvili dithered too long with a clearance kick in the final seconds inside his 22m line, allowing Nyanga to spread himself and block the ball before touching down for the crucial match-winning try, converted by Skrela.