Thomas Tuchel was not surprised Chelsea failed to keep control of their FA Cup tie with Sheffield United following a grueling run.

Chelsea were rather hanging on for much of the second half at Stamford Bridge on Sunday, though Hakim Ziyech's stoppage-time effort secured a 2-0 win, with Oliver Norwood's own goal having put the Blues ahead after 24 minutes.

The hosts have progressed to their 25th FA Cup semi-final, the third most of any club behind Everton (26), Manchester United and Arsenal (both 30), while they remain unbeaten in Tuchel's 14 matches in charge.

Chelsea have kept clean sheets in each of their last seven games – their best run since December 2005 (also seven) – while of sides within the 'big five' European leagues, only Manchester City (14) have won more games across all competitions than Chelsea (10) since Tuchel took over.

The Blues had fewer shots on target (three compared to four) than the Blades, with David McGoldrick squandering a golden chance to restore parity midway through the second half, but Tuchel revealed he was expecting a drop-off in his team's performance levels.

"It was a tough match, we had a good first half where we controlled everything but in the second we lost control, we were clearly tired," Tuchel told BBC Sport.

"I could see after the 14 matches, I could see us tire, a lack of concentration, many faults and strong opponents in the second half, so we were lucky to keep the clean sheet but I think it was the first time in 14 matches that we were lucky and allowed too many chances.

"It can happen, it's important in the end in the cup to go through. This was the target and we reached it.

"We let them come back, because we had full control in the first half, we had a big chance with Christian [Pulisic] in the second half to finish the game very early and after that we made too many easy mistakes, lost duels and lost a bit of concentration, momentum.

"Honestly I could feel it in training, some days we feel a bit tired and a lack of concentration, it's normal. It gets more problematic to keep the level up. I'm happy we got help from the bench."

It was a sentiment echoed by Pulisic, who turned in a bright performance up front for Chelsea, forcing Aaron Ramsdale into two impressive saves.

"They didn't make it easy on us," the United States international told BBC Sport.

"We knew that they had quality, we had to suffer a bit in the second half but in the end it's another clean sheet and a good performance.

"We definitely have a confident bunch of guys. Obviously, when you go on a streak like this you're feeling really good, we think we can beat anyone, it's a good feeling."