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Perhaps wary of an upset after seeing Real Madrid dumped out by minnow Albacete 24 hours earlier, Hansi Flick named a strong line-up for this meeting between the leaders of Spanish football's top two tiers, LaLiga and LaLiga 2.

Lamine Yamal, Marcus Rashford and Ferran Torres led the line for the visitors, but it was Racing that carved out the first opening as Joan Garcia had to tip Aritz Aldasoro's deflected delivery over his crossbar.

Dani Olmo was inches away from turning Rashford's centre home, while Giorgi Guliashvili's shot was too tame when Racing launched a rapid counter-attack from a Barca corner.

The visitors finally went ahead in the 66th minute, with Torres keeping his cool to round Jokin Ezkieta and tap home after being threaded through by substitute Fermin Lopez.

Ezkieta then made an excellent double save to keep out Lopez and Robert Lewandowski, with Flick introducing several more big names from the bench, but Racing had several big opportunities to force extra-time.

Manex Lozano had the ball in the net twice but was denied by the offside flag on both occasions, with the first a near-post finish on the counter and the second being a slightly more marginal call when he tapped Andres Martin's cross home.

Lozano finally timed his run to perfection in the fourth minute of stoppage-time but blasted straight at Garcia, and Racing was swiftly punished at the other end as Yamal tapped into an unguarded net to secure Barcelona's passage to the last eight.

Torres admitted Barcelona was taken by surprise by the level Racing Santander showed in the match.

"We didn't expect it to be so rocky. We had seen how they played, we were surprised that they sat off us so much," he said.

"We knew we had to stretch things and calm down. In the end, it went well.

"I think these [second-tier] teams prepare us very well for other games, they know how to do their thing very well. They have a lot of quality, that's why it's so difficult for us."

Flick, on the other hand, always expected a tough challenge.

"It was hard, and we played in a great atmosphere. The opponents did very well," Flick said. "In the end, it's 2-0, and that's what counts.

"The most important thing is that these teams are brave, they have nothing to lose, they only have things to gain and you can see that. It's fantastic to watch."

Racing head coach Jose Alberto could hardly have been more proud of his side's display. 

"We're annoyed to be eliminated, but proud to see the team playing at that level," Alberto said. "We were facing one of the best teams in the world, the difference is big."

On Lozano's late chance, he added: "He had one of the best goalkeepers in front of him. He has the personality to finish, which is what a striker has to do. 

"If he put it away, no one would say anything. I think the action was well finished, he is just an 18-year-old boy who has to grow up."