Aritz Aduriz's late stunning scissor kick gave Athletic Bilbao an opening-day 1-0 win over Barcelona in La Liga.
Last year's league champions were stunned by the late goal from the 38-year-old, which condemned them to defeat in their opening game for the first time since 2008, having already had to deal with the absence of Lionel Messi and first-half loss of Luis Suarez to a calf injury.
The visitors had twice struck the woodwork before half-time when Suarez fired against the post after intercepting a backpass and his replacement, Rafinha, later forced Simon to tip his rising effort onto the crossbar.
Athletic were worthy of the point they looked like they would pick up with Inaki Williams twice testing Marc-Andre ter Stegen, before Aduriz scored one of the goals of his career to give the Basque side a first league win over Barca since 2013.
How Athletic upset the champions
A Messi-less Barcelona looked nervous with their gameplan for a good 15 minutes while Athletic Bilbao set about finding a valuable opener.
But for two fine Ter Stegen saves from Williams they would have got it, and the striker certainly should have done better when played in behind by Yuri Berchiche down the left, but he shot straight at the goalkeeper's legs after cutting inside.
Barcelona struggled to create chances but still came closest before the break. First a horror back-pass played blind by Unai Lopez set Suarez through, but the post denied the Uruguay striker with only Simon to beat.
He would get no chance to remedy that miss as he limped off injured before the break, but his replacement was a whisker away from opening the scoring in the dying moments of the first half when his rising effort from the edge of the box was tipped onto the bar by Simon.
The first half had been a relatively lively affair considering the scoreline, but the second struggled to live up to it.
Ernesto Valverde introduced Ivan Rakitic at the break, but Barcelona still struggled to find a cutting edge against a home side increasingly willing to settle for a point.
But with less than 90 seconds to play, substitute Aduriz popped up with a stunning winner as he adjusted to meet Capa's cross with a perfect scissor kick which caught Ter Stegen out and sent the San Mames into raptures, and Barcelona facing a shock opening-day defeat.
Barcelona's woes were compounded by the news that Suarez faces an unspecified length of time on the sidelines due to the right calf injury he sustained in the defeat - with their pursuit of former forward Neymar still in the balance.
Analysis: Barcelona in a Mess-i without Lionel
Sky Sports' Ron Walker:
Even before Suarez hobbled down the tunnel there were worrying signs for Ernesto Valverde, whose side looked rudderless in attack without Messi just as they did last season when he was missing.
You would have expected Antoine Griezmann to be up to speed after a full pre-season at the Nou Camp but he looked isolated on the left, and only improved when he was moved inside after Suarez's injury.
Losing was harsh on Barcelona in the end as they kept Athletic at bay for most of the second half, but they look a million miles from the dominant sides who have swept away everything in their path in years gone by.
Personnel must be a major concern for Valverde, whose answer to the need for a late winner was to introduce Carles Perez from the bench, despite having just 17 minutes of first-team football under his belt.
Perhaps the head coach was complacent in starting Sergio Busquets and Ivan Rakitic on the bench, before introducing the latter at half-time, but the performance of their replacements Carlos Alena and Sergi Roberto will only cement any concerns he has that this Barca squad is lacking depth.