Not even the return of Lionel Messi from a three week injury layoff could stop Barcelona from being upset at home by Real Betis on Sunday, with the La Liga leaders falling 4-3.

Messi, who had been sidelined since hurting his arm against Sevilla on Oct. 20, was involved in all three of Barca’s goals. His 68th minute penalty brought the hosts back within one after Betis jumped out to a 2-0 lead in the first half, and the Argentine set up Arturo Vidal before adding another himself in stoppage time. But it was too, little too late, mainly because of Barcelona’s atrocious defending.

Betis peppered Marc-Andre ter Stegen’s goal with 15 shots, eight of them on frame. And Barca were unable to gain any momentum from Vidal’s strike or Messi’s spot kick, as Barca almost immediately allowed Betis to score again. The visitors’ third was the result of an error by Ter Stegen. It was a historically dreadful performance overall: Sunday’s match marked the first time that Barca had conceded four times at home in 15 years. It also handed Betis its first win at the Camp Nou in two decades.

Fortunately for Barcelona, the shoddy defensive showing appears to be an outlier. Barca, which remains atop the Spanish top flight despite the loss, had conceded just 10 times in 10 games coming into Sunday’s contest. Their biggest concern was actually at the opposite end of the field, with Ernesto Valverde’s team, minus Messi, scoring significantly fewer goals than at the same point last season, when they won the title by 14 points.

The timing isn’t good, as Messi and Co. will have to wait to shake the losing feeling. Because of the upcoming international break, Barcelona won’t be back in action for another two weeks. Their next match is a tough one, too, away to 2017-18 runner Atletico Madrid on Nov. 24.

Doug McIntyre covers soccer for Yahoo Sports. Follow him on Twitter @ByDougMcIntyre.

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