Dembele had been sidelined since September after suffering a hamstring injury in just his third appearance for the club following his move from Borussia Dortmund.

He was given the all-clear to return to action earlier this week, though, and came on for the final 20 minutes against Celta at Balaidos.

The 20-year-old Frenchman was unable to find a winner on the night, but Barca -- looking to win the cup for a fourth successive year -- will nevertheless be optimistic of progressing to the quarterfinals in next Thursday's second leg at the Camp Nou.

Ernesto Valverde's men had enough chances to have finished the tie off this evening, but in the end only had Jose Arnaiz's 15th-minute strike to show for their efforts.

Barca B striker Arnaiz, leading the attack in the absence of star names Lionel Messi and Luis Suarez, scored in his third successive cup appearance when he finished off a low cross from Andre Gomes.

That lead lasted just 16 minutes, however, before Celta drew level through Pione Sisto's thunderous finish.

Iago Aspas was unlucky to see his effort come back off the underside of the bar and bounce away off Jasper Cillessen's knee, but Sisto latched on to the loose ball and, despite the narrow angle, thrashed a rising shot back past Barca's Dutch goalkeeper.

Celta have been a bogey side for Barca in recent years, beating them three times in their last seven meetings and holding the La Liga leaders to a 2-2 draw at the Camp Nou recently, but it was the visitors who could have put the game to bed.

Arnaiz was unable to make the most of two clear chances at the start of the second half while Denis Suarez also spurned a good goal scoring opportunity.

Sergio Busquets then rattled the Celta crossbar from outside the box as Barca tore into their opponents after the interval.

The hosts responded with Emre Mor twice going close before Barca resumed their bid for winner only to see Dembele denied by home goalkeeper Sergio Alvarez and, in stoppage time, hit the woodwork again through Sergi Roberto.