Barca forward Jose Arnaiz, who usually plays for the reserve side, poked in Andre Gomes's low cross to complete a sweeping counter-attack and put Barca ahead in the 15th minute, scoring for the third Cup game in a row

Denmark international Pione Sisto levelled for Celta in the 31st, smashing the ball into the roof of the net on the rebound after Iago Aspas had hit the underside of the crossbar.

Barca's record signing Ousmane Dembele came on in the second half to make his first appearance since rupturing his hamstring in September and nearly scored the winner, but his low shot was saved by Celta goalkeeper Sergio Alvarez.

Barca hit the woodwork twice, Sergio Busquets crashing a shot against the bar and Sergio Roberto striking the post in stoppage time while Turkish international Emre Mor went close to grabbing a winner for Celta.

Barca have now failed to win on their last three visits to Celta's Balaidos stadium, losing 4-3 and 4-1 in their last trips in La Liga.

Coach Ernesto Valverde made seven changes to the Barca side that beat Real Madrid 3-0 in their last game while Celta, coached by former Barca assistant Juan Carlos Unzue, fielded a full-strength team.

The second leg at the Nou Camp takes place on Jan 11.

Champions Real Madrid visit second division Numancia later on Thursday.