Osasuna finding themselves 2-0 ahead.After being picked out by Garcia on the right flank, Alvaro Cejudo looped in a cross which found the surging Lekic, and the Serbian tapped past Valdes for his second of the match.
Barcelona did pull one back five minutes into the second half, with Isaac Cuenca responsible.The half-time substitute centred a cross from the right and found Alexis Sanchez unmarked, with the Chile international sliding the ball past Osasuna goalkeeper Andres Fernandez.
But the home side soon had a third goal when Garcia netted to give Osasuna a decisive advantage.The reigning champions refused to give up without a fight, as another substitute, Christian Tello, made it 3-2 with 18 minutes remaining.
In other matches, Racing Santander played out a 0-0 draw in their match at home to Atletico Madrid.
Finally, Nelson's 91st-minute strike saw Real Betis snatch a 2-1 win at home to 10-man Athletic Bilbao.
Ruben Castro opened the scoring for hosts Betis 10 minutes into the match Estadio Benito Villamarin, with Javi Martinez pulling one back for Athletic.
Athletic were reduced to 10 men when goal-scorer Martinez committed a second bookable offence in the 64th minute.
