Barcelona followed up last weekend's 3-1 defeat at Real Madrid with another reverse on Saturday that cost them the lead in La Liga, squandering a host of chances to lose 1-0 at home to Celta Vigo.
Barca forward Neymar hit the crossbar twice and team mate Lionel Messi did likewise once before hesitation in the defence let in forward Joaquin Larrivey to score 10 minutes after halftime at the Nou Camp.
Messi, who remains one goal short of La Liga's scoring record of 251, sent a free kick against the corner of the goal frame in the 80th minute. Luis Suarez, making his home debut, was then denied by a brilliant save from Celta goalkeeper Sergio as Barca strove in vain for an equaliser.
Barca's second straight defeat means Real take over at the top on 24 points from 10 matches thanks to a 4-0 win at Granada earlier on Saturday.
Champions Atletico Madrid, 4-2 winners at home to Cordoba, are second on 23 points.
Sevilla can overtake Real and Atletico with victory at Athletic Bilbao on Sunday.