The first chance of the game fell to the visitors as Goncalo Guedes dragged wide from the edge of the box after just four minutes.
Moments later, he was shown how to finish by Abderrahman Rebbach, who was fed the ball 25 yards from goal after Denis Suarez was sent galloping away down the right. The Algerian’s low shot crept into the net despite Alex Remiro getting a hand to it.
Their lead didn’t last long though as, on the quarter-hour mark, Guedes redeemed himself with a smart pass to pick out Mikel Oyarzabal after Alaves failed to clear a corner. La Real’s captain proceeded to finish clinically from a narrow angle to level the game.
After Carlos Soler curled his effort over the top, Pellegrino Matarazzo’s men shot themselves in the foot and gifted the hosts their lead back when Benat Turrientes clumsily bundled Jonny Otto to the ground in the box. Toni Martinez stepped up and buried the spot kick low to Remiro’s left.
Just after the break, Brais Mendez teed up Guedes for another chance but the Portuguese international was denied from close range by Raul Fernandez.
Chances were scarce after this, but Duje Caleta-Car gave Martinez another chance from 12 yards in comical fashion as he pulled the former West Ham striker’s shirt over his head in the box. Martinez stepped up again and went the same way but Remiro was ready this time and made the save.
That miss proved to be crucial as, with a quarter hour remaining, Guedes finally got his goal. The former Wolves man was slid in behind by a lovely ball from Turrientes but with work still to do, he did it immaculately with a confident finish low across Fernandez into the far corner.
Things got better for the visitors as just five minutes later, with just 10 minutes of normal time left, two substitutes linked up as Orri Oskarsson was sprung clear by Luka Sucic and the Icelandic forward squeezed the ball through the legs of the onrushing goalkeeper to give his side their first lead of the night.
It would be the only lead they would need as the Txuri-Urdin marched on to the semi-finals after an enthralling encounter.
Flashscore Man of the Match: Goncalo Guedes (Real Sociedad)
