Thomas Tuchel admitted Chelsea were fortunate to see off Sheffield United 2-0 to reach the FA Cup semi-finals.
Oliver Norwood's own goal and Hakim Ziyech's last-gasp strike sealed Chelsea's quarter-final win at Stamford Bridge as Tuchel extended his record unbeaten start in west London to 14 matches.
David McGoldrick and Rhian Brewster spurned fine chances for the visitors, who paid the full price when Ziyech broke and finished in style.
Chelsea boss Tuchel conceded his players rode their luck but praised the Blues for fighting past the mental and physical tiredness of beating Atletico Madrid on Wednesday.
"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. "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.
- Chelsea 2-0 Sheffield United - Match report
- How the teams lined up | Match stats
- FA Cup fixtures | Results
- Get Sky Sports | Get a Sky Sports Pass
"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."
Tuchel answers international break questions
Chelsea head into the international break on a major high, sitting fourth in the Premier League - and now with an FA Cup semi-final to add to their Champions League quarter-final.
Tammy Abraham missed Sunday's clash having suffered a repeat of his niggling ankle injury, while Edouard Mendy will now not head off on international duty with Senegal.
"Tammy quit training yesterday after only five minutes," said Tuchel. "There was no chance for him to join the squad. It's more or less the same injury, a re-injury due to a training accident in almost exactly the same spot.
"He was in pain and he had to quit training after five minutes. Hakim Ziyech will go off on international duty like everyone else.
"But Edouard Mendy will stay, because he has to see the dentist for an operation on his tooth, and this absolutely has to be done now."