Barcelona's title ambitions were dealt a further blow as they were beaten 2-1 at home by Valencia, suffering a third consecutive league defeat for the first time since 2003.
An own goal by Ivan Rakitic gave Valencia a shock lead on 27 minutes and Santi Mina doubled their advantage just before the break.
Lionel Messi scored his 500th career goal for club and country to reduce the deficit midway through the second half, but was unable to inspire a comeback.
Barca remain top of the Primera Division on 76 points but are only ahead of Atletico Madrid due to their superior head-to-head record. Just three weeks ago they led Diego Simeone's side at the top by nine points.
Sunday's result means Barca have now picked up just one point from their last four league games and, if that was not bad enough, they were also knocked out of the Champions League quarter-finals by Atletico in midweek.