Barcelona coach Flick urges players to keep focus after 4-0 lead against Dortmund

Barcelona thrashed visitors Borussia Dortmund 4-0 in their Champions League quarter-final first leg on Wednesday but their manager Hansi Flick was quick to silence suggestions that his side had already booked their place in the semi-finals.

Flick played down Barca's sizeable lead ahead of next week's return visit to Germany.

""No, no, no, no, no, no, no, no... We are definitely not qualified yet! You never know what's going to happen because football is just a crazy sport," Flick told Movistar Plus.

"To advance we have to play in Dortmund like we did today, without making mistakes. We played very well and when you play like that you score goals, which is what happened."

Undefeated since late December, treble-chasing Barca were once again boosted by brilliant performances of their attacking trio.

Robert Lewandowski netted twice against his old club after Raphinha opened the scoring, while Lamine Yamal wrapped up the win, but Flick also heaped praise on his defender who managed to keep a clean sheet.

"(Lewandowski, Yamal and Raphinha) are brilliant and very important for us, but so is our defence and those who come in from the bench," Flick told a press conference.

"They have been showing that they can quickly make an impact and reach the same level as those who were on the pitch from the start.

"At this point of the season, with this schedule, it's so important that we keep all the legs fresh. So the team's depth is key.

"We played at a very high level, but we did make some mistakes and we can improve. Dortmund have very fast players but we defended really well. I am very happy."