Athletic Bilbao have wasted a two-goal advantage as Zilina fought back to claim a 3-2 victory in the first leg of their Europa League playoff tie.
Zilina offered very little going forward for long spells of the match, and it appeared that an emphatic win was on the cards when Ibai played an inch-perfect pass through to Sabin Merino, who held his nerve to find the bottom corner.
Despite removing a number of key players from the starting lineup following the Spanish Super Cup triumph over Barcelona, Ernesto Valverde's side looked capable of killing off the tie, with Sabin missing a good chance when he headed over from Inigo Lekue's cross.
The lead was doubled just after the half-hour mark when Kike Sola drifted into space in the box, before capitalising on poor marking to fire past Milos Volesak.
Bilbao appeared to be comfortable either side of the half-time interval, but Zilina managed to pull a goal back midway through the second half when Jakub Paur was given the room to unleash a shot which deflected off Lekue on the way in.
Zilina still looked vulnerable at the back after reducing the deficit until Bilbao were left stunned by an equaliser from William, who beat the offside trap with a perfectly-timed run before rounding Iago Herrerin to slot home.
Bilbao threatened to score a potentially crucial third away goal late on when Inaki Williams sent a decent chance just over.
There was still time for a late twist, though, as William took advantage of hesitancy in the Bilbao defence to collect a loose ball and fire past Herrerin in stoppage time to hand Zilina a slender advantage ahead of next week's second leg.
