Cristiano Ronaldo says Real Madrid must be wary of a Spurs onslaught despite taking a 4-0 lead to White Hart Lane next Wednesday.
Real and Barcelona now seem destined to meet in a classic semi-final showdown after both sides enjoyed runaway first-leg victories in the first legs, but Ronaldo is taking nothing for granted.
He said: "We've taken a huge step but we have to play in London and we can't underestimate Tottenham. In the second half we showed our superiority, touching the ball and looking for goals. We should congratulate ourselves because it's a great result.
"I am happy because the team played well and 4-0 in the quarter-finals of this competition is very good. Even so, we have to continue to work and make use of our advantage - but anything can happen in football.
"Regardless of whether we played against 10 men, the team played well. The first half was a bit difficult but we improved significantly in the second half."
Xabi Alonso added: "I know their ground well. It's one of the grounds I liked the most in England. Despite the 4-0, their fans will support them to the death. If we do well and control the game from the start we'll have an easy night. But if they find a bit of life they can complicate things for us so we shouldn't take anything for granted.
"You never know what can happen in football but it's true that we have to play very, very badly and they have to play very, very well."