Chelsea continued their unbeaten start to the season with a 3-0 victory over Dean Smith’s men thanks to Romelu Lukaku’s brace and Mateo Kovacic’s strike.
Saul, a summer transfer deadline day loan signing from Atletico Madrid, was handed a starting berth ahead of Jorginho but the Spaniard failed to stamp his authority on the game and was replaced at half time by the Italian.
Saul was guilty of losing possession on a number of occasions, misplaced simple passes and was bullied by the Villa midfielders as he was given a taste of what the Premier League is all about.
Tuchel has acknowledged that Saul did not have his best game and has taken responsibility for that.
'It was a hard decision but I had the feeling he struggled,' said Tuchel. 'There were some big mistakes, passing mistakes, easy ball losses which is very unusual for him. He struggled with the intensity. You could see he isn't fully adapted.
'Hopefully he can accept it was completely my responsibility. I had the feeling he could jump in and play at that level.
'I put him into a very difficult match after the international break and it was hard to adapt the physicality in general, and to the intensity and high pressing of Aston Villa. Also it was hard for him to adapt to our system and principles.
'I thought it was maybe better to change him and to give us more stability in the centre and switch the shape.'
Chelsea have the option to make Saul’s move permanent for £30m at the end of his loan spell.
