Messi scored twice, with Alba, Luis Suarez and Ivan Rakitic also on target as Barca won 6-1 on aggregate and extended their unbeaten streak to 28 matches in all competitions.

Alba set up both of Messi's goals in two first-half minutes before the Argentine returned the favour, creating the third goal for the left-back with a wonderful through ball.

"Messi is the best player in history and the best in the world by a difference," Alba told reporters after the game.

"It's a luxury to have him here. All Barca fans should enjoy him, as I think they are doing. He's been here for 12 years playing at a spectacular level and this year he's been even more incredible."

Alba has now set up seven of Messi's 22 goals this season, while Messi has set up both of Alba's strikes.

It's a relationship which has only really blossomed in the last six months, with Neymar's move to Paris Saint-Germain allowing Alba much more space on the left.

In his previous five seasons with the club, he had only set up five goals for Messi.

"It's incredible how [Messi] reads the game, especially for me," Alba added. "We always look for each other and we were both able to get on the score sheet today. I hope that our connection continues like this forever."

Celta coach Juan Carlos Unzue -- Luis Enrique's assistant at Barca for the past three seasons -- lamented his side's inability to shut down a partnership which has been so lethal this season.

"We just weren't capable of defending the Messi-Alba binomial, a link up which we have seen many times and in the La Liga game here last month we were able to stop it," Unzue said in his postgame news conference.

"We are seeing a lot of them this season, but it makes sense because there is no winger on the left anymore and there is room for [Alba] to surprise from deep."

Suarez added Barca's fourth goal, his 12th of the campaign, after a mistake from Pione Sisto as Ernesto Valverde's side went into half-time with a commanding lead.

Valverde took the chance to take off Messi, Andres Iniesta and Gerard Pique after the break, with the fifth goal eventually arriving in the final minute when Rakitic headed home Ousmane Dembele's corner.

Barca join Real Madrid, Atletico Madrid and Valencia in the draw for the quarterfinal, which will take place on Friday.

"I would say I'd prefer not to draw Real Madrid," Valverde admitted in his news conference after the game. "But I shouldn't say that because it will mean we'll draw them!"