A dramatic winner from Fernando Llorente with two minutes to go sent Athletic Bilbao through to the Europa League final, where they will face fellow Spanish side Atletico Madrid.
Llorente prodded home at the near post to make it 3-1 to Athletic, 4-3 on aggregate, just when it looked as though Sporting Lisbon would take the semi-final to extra-time.
Earlier, Markel Susaeta put Athletic ahead in the 17th minute but after the home side had missed several gilt-edged chances, Dutch striker Ricky van Wolfswinkel equalised in the 44th minute with a snap-shot from the edge of the penalty area. Less than a minute later Marco Bielsa's side were back in front when Llorente's sublime drag-back set up Gomez Ibai.
Leading 4-2 from the first leg, Atletico made sure of their progress to the final when Adrian scored on the hour to beat Valencia 1-0 in the Mestalla.