Well, the Catalans lost 2-1 in a rematch of the European Super Cup, undone by some bad luck, poor finishing and stellar play from a Sevilla side who'd struggled to begin the new campaign.
Neymar, counted on to pick up the slack along with Luis Suarez in Messi's absence, indeed scored in the 74th minute but Sevilla did the damage earlier, getting goals from Michael Krohn-Dehli in the 52nd minute and Vicente Iborra in the 58th in Seville.
"It was a game in which we had a lot of chances," Barcelona manager Luis Enrique was quoted as saying by Barcelona's website. "It's almost unbelievable that we walk out of here with just one goal.
"Ten minutes in the second half ... hurt us."
In losing its second league game of the season, Barcelona missed a chance to leapfrog Villarreal atop the standings. Barcelona lost four league games all of last season en route to completing a treble of titles.
"We had chances to win the game," Suarez was quoted as saying by Barcelona's website. "But it's not the end of the world, either.
"Obviously we're the best team in the world, but the players are experienced and nobody in particular has to take the blame, just like when we won everything, it was as a group.
"In these games mistakes end up haunting you, which is what everyone saw."
Barcelona -- also without Andres Iniesta and Dani Alves -- and Sevilla engaged in an often end-to-end encounter, similar to the Super Cup, won 5-4 by Barcelona in August.
Barcelona keeper Claudio Bravo was forced into action in the early going, and Suarez should have done better when set up by Neymar. Those sequences set the tone. Neymar struck the post with a free kick -- Gerard Pique was prevented a tap in on the rebound thanks to a block -- and Suarez hit the woodwork with a looping chip.
But Sevilla hung on until halftime, scored its goals and hung on again following Neymar's penalty in the 74th. Sandro almost levelled, but he, too, hit the post.
"We have to pick ourselves up," added Barcelona midfielder Ivan Rakitic. "Every team has their lows."
Villarreal travels to Levante on Sunday but the highlight is the Madrid derby between Real Madrid and Atletico Madrid.