Barcelona conceded twice in 68 seconds and Real Madrid were blown apart at halftime as La Liga’s two title favourites were each stunned by surprise defeats on Wednesday night.
By the end, Atletico Madrid, who had cruised to victory over Huesca on Tuesday and play Real on Saturday, were the biggest winners, and they will jump above Real with a win at the Santiago Bernabeu.
Gerard Pique committed the decisive blunder, his fluffed clearance allowing Oscar Rodriguez to score Leganes’ second goal in two incredible minutes at Estadio Municipal de Butarque.
Nabil El Zhar had nodded in an equaliser moments before and by the end Philippe Coutinho’s sumptuous early volley was reduced to little more than a footnote.
After drawing at home to Girona on Sunday, albeit with 10 men, Valverde’s selection also came under scrutiny, after he opted to rotate for the second time in three days.
Barcelona face Athletic Bilbao on Saturday and then Tottenham at Wembley in the Champions League four days later but one point from two of La Liga’s lesser opponents is a concern.
So is the form of Pique, who was also at fault against Girona and will almost certainly start against Spurs, with Umtiti suspended.
Real Madrid, who were just kicking off as Leganes closed out, could have pulled three points clear at the top but instead were three down at halftime.
Twice Jesus Navas sped away on the counter-attack, and twice he found Andre Silva, the first time with a deliberate cut-back, the second when his shot was palmed out for a rebound.
Wissam Ben Yedder added a third six minutes before the interval, volleying in from close range after the Madrid defence had pushed out.