Iñaki Williams struck in stoppage time to send Athletic Club into the Copa del Rey semi-finals for the sixth time in seven seasons, sealing a dramatic 2-1 victory over Valencia at a packed Mestalla.

The tie brought together two former Spanish heavyweights enduring difficult LaLiga campaigns, with both sides viewing the cup as a vital opportunity to revive their seasons.

Valencia started brightly and almost took an early lead through Luis Rioja, but it was Athletic who opened the scoring in fortunate circumstances. From Robert Navarro’s free-kick, Umar Sadiq inadvertently headed the ball into his own net following a mix-up with Dimitri Foulquier, handing the visitors a surprise advantage.

Defensive errors continued to shape the first half, and Sadiq atoned for his earlier mistake when he capitalised on Alex Padilla’s spilled effort. The Nigerian reacted quickest to Rioja’s shot, slotting home the rebound to level the scores.

The contest ebbed and flowed as half-time approached, with Athletic pressing for a response. Mikel Jauregizar went close with a diving header from Navarro’s cross, but his effort drifted wide.

After the interval, clear chances became scarce as both sides struggled to find the decisive moment, and extra time appeared increasingly likely. Nico Serrano was Athletic’s main attacking outlet, though his speculative efforts failed to test Stole Dimitrievski.

At the other end, Foulquier came closest to breaking the deadlock when his close-range strike crashed against the post following an impressive passing move.

Late drama followed when Athletic were awarded a penalty after a lengthy VAR review ruled that Cesar Tárrega had handled the ball inside the area. However, Jauregizar failed to capitalise, seeing his weak spot-kick comfortably saved by Dimitrievski, much to the delight of the home crowd.

As the match edged toward extra time, the Williams brothers stepped up to decide the contest. In stoppage time, Nico’s surge down the flank set up Iñaki, who calmly finished to secure Athletic’s place in the last four.

The victory extended Athletic’s impressive record in the competition, marking their eighth consecutive away win in the Copa del Rey and underlining their enduring cup pedigree.

For Valencia, meanwhile, the defeat represented another setback in a difficult season, bringing an end to their six-match unbeaten home run in all competitions.