Their problems began when Luis Suarez was taken off injured a few moments later and they collapsed in the second half
La Liga champions Barcelona's long winning streak came to an abrupt halt when they suffered a shock 3-1 defeat away to Levante on Saturday after taking the lead but then conceding three times in the space of seven minutes in the second half.
Barca had returned to the top of the table by thrashing Real Valladolid 5-1 in mid-week for a seventh straight victory in all competitions and put themselves in a comfortable position when Lionel Messi converted a penalty in the 38th minute.
Their problems began when Luis Suarez was taken off injured a few moments later and they collapsed in the second half, with Levante scoring with all of their first three shots on target.
Jose Campana levelled in the 61st minute following a quick-fire counter-attack after winning the ball in Barca's half, then former Real Madrid striker Borja Mayoral put them ahead in the 63rd with a superb curling strike from outside the area.
Nemanja Radoja gave the home side extra breathing space with a third goal in the 67th on the volley following a free kick, while Messi put the ball in the net later to briefly give Barca hope but the goal was ruled out for offside by Antoine Griezmann after a VAR review.
It was Barca's third defeat of the campaign yet they still lead the standings on 22 points and a superior goal difference over Real Madrid, who were held to a goalless draw at home to Real Betis and are second on the same number of points.
Atletico Madrid are third on 21 after drawing 1-1 away to Sevilla, who are fourth, also on 21.
Levante, who have won three of their last four home fixtures against Ernesto Valverde's side, moved up to eighth in the table on 17 points.
"It was an even game but they took advantage of those seven minutes. It wasn't a great performance from us but the result is excessive," Barca midfielder Sergio Busquets told reporters.
"We didn't create much but in the second half we did ourselves a lot of harm with that spell when they scored three times.
"We're going to try and stay positive, we were on a great run which has now been broken but we're still top and we have a lot more games to come."
Barca coach Valverde made four changes to his team from the Valladolid game, bringing 120-million-euro signing Griezmann back into the line-up at the expense of teenager Ansu Fati while starting without Busquets, Jordi Alba and Arthur.
The manager, who has won the title with Barca for the last two seasons, was asked after the defeat if he was considering his position but emphatically ruled out stepping away.
"Of course I'm not thinking about that, this is only one defeat. We have to react, we always do and it won't be any different this time," he said.
"Our aim was to try and go for a second goal after taking the lead but we weren't able to create enough danger. We lacked organisation after the second half and had little control."
Griezmann struggled to explain Barca's collapse after the interval.
"When you concede three goals in a few minutes then it could be a problem of everything, attitude and our style of play. We have to do everything to stop this happening again," said the French forward.
"We didn't start the second half well but there's nothing we can do about it, we can only improve and learn. Anything can happen in a game but it's how you react, and we didn't react properly today."