With his side twice squandering the lead over the course of the match, Messi’s frustrations boiled over in the game’s closing moments as he petulantly swung an arm at Asier Villalibre.
There had been some cause for optimism at Barcelona in recent weeks, with a string of improved performances helping the Catalan club climb to third in La Liga.
Koeman was looking for his first trophy as manager and his side got off the best possible start, with Antoine Griezmann giving Barcelona the lead five minutes before half time.
However, the advantage lasted just two minutes as Oscar de Marcos stole in behind Barcelona’s static back line to turn home Iñaki Williams’ cross.
Despite Bilbao having the better of play in the second half, Greizmann appeared to have given Barcelona the winner with just 13 minutes remaining, only for Villalibre to equalize in the game’s final minute.
It took just four minutes of extra time for Bilbao to find the winning goal, with Williams curling home a stunning strike off the post to give the Basque club its first major trophy since it won this same competition back in 2015.
Things would still get worse for Barcelona as Messi’s late act of violent conduct was picked up by VAR, meaning the Argentine could now miss the next four domestic matches.
It was Messi’s first red card in Spanish football since being sent off 15 years ago for Barcelona B against Peña Sport, with the only other red cards of his career both coming for the Argentine national team.
Juve and Ronaldo stumble
Juventus has been crowned Serie A champion for nine consecutive seasons, but it would appear the Turin club’s stranglehold on the Scudetto could finally be coming to an end.
The Old Lady was beaten 2-0 by Inter Milan thanks to goals from Arturo Vidal and Nicolo Barella, as Antonio Conte’s side moved level on points with city rival AC Milan at the top of the table.
There had been some controversy involving Vidal prior to kick off, as video footage appeared to show him kissing the Juventus badge on Giorgio Chiellini’s chest as he greeted his former teammate.
Vidal spent four years at Juventus between 2011 and 2015, winning seven major titles during his time at the club.
After the game, Vidal denied intending to kiss the badge and there was certainly no questioning the Chilean’s loyalty once the match had started as his thumping header gave Inter a deserved lead.
Barella secured the three points in the second half as Juventus stays in fifth place, now seven points behind the two Milan clubs.
The win was also Conte’s first in the Derby d’Italia as Inter boss, having previously managed Juventus between 2011 and 2014.