Sevilla conceded a 90th-minute goal to fall to a 1-0 defeat at home to Athletic Bilbao on Monday, delivering a near fatal blow to their La Liga title hopes.
Julen Lopetegui's side dominated the game but were dealt a late body blow when Athletic counter-attacked and striker Inaki Williams showed composure to lift the ball into the top corner.
The goal inflicted a first defeat on Sevilla since March 6 and snapped a five-game winning streak in La Liga which put them among the contenders in the close-run title race.
The loss left Sevilla fourth in the standings on 70 points with four games to play, four behind second-placed Real Madrid and third-placed Barcelona and six from leaders Atletico Madrid.
Coach Lopetegui felt his side were hard done by and was angry about not being awarded a penalty early in the second half when the ball struck the hand of Athletic defender Mikel Balenziaga.
"We could easily have been awarded a penalty, we didn't have any luck," he told reporters.
"We have won many games with far fewer chances than we had tonight. But we have earned the right to dream of the title and we'll keep going."
Sevilla have a chance to get back into contention when they visit Real Madrid next weekend.
Athletic celebrated a second win in eight days over a title contender, having beaten leaders Atletico 2-1 at home last Sunday.
The Basques could yet have another say in the title race when they host Real Madrid on May 16.
Sevilla made a rampant start and had their first chance when Lucas Ocampos slid in to meet a cross but could not keep his shot under the bar.
Sevilla forward Youssef En-Nesyri had a clearer opportunity midway through the first half but his header was blocked by a low save from Spain keeper Unai Simon, who thwarted the Moroccan again before half-time, parrying his shot and then scurrying back to prevent the ball from trickling over the line.
Athletic had their first chance early in the second half when striker Asier Villalibre manoeuvred his way through the hosts defence but flashed his shot just wide.
Sevilla were furious for not being awarded a penalty when Balenziaga's hand blocked a cross from Jesus Navas and they continued to cause plenty of danger but seemed to lose confidence every time they got close to the goal.
Down the other end, Athletic substitute Nico Williams helped force the ball over the line but the goal was ruled out for offside.
A few moments later his older brother Inaki had better luck, scoring for the first time since February as he delivered a sucker punch to Sevilla.
"It's a very tough blow. We tried everything, we had a lot of chances and then they had one opportunity and scored," added Sevilla captain Navas.
"But we're going to keep on trying, we're going to fight in every game and we're going to Madrid next week to win."