Thomas Tuchel revealed he suspected Chelsea might be short of their best against Sheffield United.
The 2-0 win took them through to the semi-finals of the FA Cup and means they remain unbeaten in their 14 matches since the German took over as Blues boss.
But they endured a difficult second half at Stamford Bridge, where the Blades had chances before Hakim Ziyech’s injury-time goal sealed the win.
Chelsea, through the quarter-finals of the Champions League following their recent win against Atletico Madrid, have still not conceded a goal at home under Tuchel.
“It was the 14th match in a row and I could feel after the game against Atletico that we were a bit tired,” Tuchel said.
“I could feel that this was a huge effort – also mentally – against Atletico and after that a big relief.
“There was also a moment yesterday when we prepared for the match and today where I did not feel 100% comfortable or sure that we could continue on the same level.
“I even spoke to the team before and said ‘Let’s not over-expect from ourselves in this situation – do a serious performance and try to control the match’.
“The first half was OK. In the second half we lost control.
“But it is absolutely OK. After 14 matches the target was to go to the quarter-finals (of the Champions League) and to Wembley (for the FA Cup semi-finals) and the team achieved both targets.”
The win means German Tuchel will make his first-ever visit to Wembley.
“I don’t think I’ve ever been to Wembley before, so I’m very excited,” he said.