Rafael Benitez has warned his Chelsea side against any complacency if they want to see off Basel and reach the Europa League final.
Blues won 2-1 in the Swiss city
thanks to David Luiz's late free-kick but Benitez remains wary of the threat they pose in the return leg on 2 May.
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“We are working so hard and when you win these kind of games the mood and feeling is much better, we have to keep the positives and try to keep the momentum”
"We must concentrate and have no over-confidence for the next game," he said.
"They can score goals at home and away. If we play well we can beat anyone so we have to do it."
Basel beat Tottenham
on penalties in the quarter-finals.
They led 2-0 in the first game at White Hart Lane before being pegged back to draw 2-2, the same scoreline as their second leg in Switzerland.
Benitez added: "We have the experience of Tottenham so we know that this team is a very good team."
Chelsea took an early lead through Victor Moses at St Jakob Park but wasted chances before Fabian Schlar equalised with a dubious penalty after Cesar Azpilicueta was adjudged to have fouled Valentin Stocker.
Benitez felt that the sense of injustice at the spot-kick helped spur his team on.
He said: "The penalty was a surprise to everyone but in the end the second goal was good enough for us.
"It wasn't [a penalty]. To give a penalty it has to be very clear. We had the feeling that we didn't deserve to concede so it was extra motivation. You can say we were lucky but we scored a goal and everybody thought it was a fair result.
"We are working so hard. When you win these kind of games, the mood and feeling is much better. We have to keep the positives and try to keep the momentum."
Ashley Cole will miss next week's second leg after being given a yellow card for time-wasting.
But Benitez is confident Ryan Bertrand will have no problems filling in.
He added: "I was surprised with the yellow card, it was too quick but Ryan is doing well anyway."