Chelsea boss Thomas Tuchel admits his side was a little fortunate to secure a win at Sheffield United.
The Blues were in absolute control for much of the FA Cup quarter final against the bottom of the league Blades.
Sheffield United, nevertheless, put up a good fight for spells, and came close to equalizing through David McGoldrick and Rhian Brewster.
Chelsea now face Manchester City in the semi finals, with Leicester City facing Southampton for a place at the Wembley showpiece.
“On the 14th match in a row, I could feel us after the Atletico game a bit tired, there was a big relief in the team, and that is absolutely normal,” said Tuchel to reporters.
“It was also a huge effort mentally against Atletico.
“Then you have a lot of changes, made from me of course, and you have players leaving right now for international duties, so there is a lot to organise, and many unclear situations.
“It was a moment where we arrived yesterday where I didn’t feel 100 per cent comfortable or sure that we could continue on the same level.
“I said to the team before, don’t over-expect from ourselves in the situation. Put in a serious performance, take the little details, but don’t over-expect.
“The first half was okay, the second half when there was the chance for Christian Pulisic that we didn’t take, then we lost control, concentration, a bit of momentum and there were many minutes we had to suffer.
“They had two big chances and we were lucky to escape with a clean sheet. But there are a lot of circumstances to explain it, and it’s OK.
“After 14 matches the target was to go to the quarter-finals [of the Champions League] and to Wembley, and the team have achieved both of the targets so big compliments to them and well done.”