City were favourites going into the game in Porto, Portugal but Kai Havertz gave Chelsea a deserved lead midway through the first half and the Blues held out against a below-par City side.
Guardiola routinely deploys a defensive midfielder and has switched between Rodri and Fernandinho all season, depending on the pair’s fitness and suitability to City’s opponents.
However, the Spaniard opted for an ultra-attacking line-up that saw Ilkay Gundogan play in a deeper role behind Bernardo Silva and Kevin De Bruyne in midfield, with Raheem Sterling, Phil Foden and Riyad Mahrez in attack.
The move backfired, with Chelsea quietening City’s attack and breaking well on the counter-attack.
Guardiola has been accused of tinkering following his side’s defeat but he insists he has no regrets about his decision to go without a defensive midfielder.
‘I decided the decision, to have quality players. Gundogan played many years in this position,’ said Guardiola.
‘To have speed, to find the small players, the quality, the brilliant players, inside, in the middle and between the lines. This was the decision.
Asked if he regretted his decision, Guardiola said: ‘I don’t know – the decisions I made, the players did everything to try to win the game.’
Tuchel admitted after the game that he was surprised by Fernandinho’s omission from the starting line-up.
‘I expected Fernandinho in the line-up. He chose a very offensive, technical line-up, very hard to steal the ball and recover the ball. Everything else we pretty much expected,’ said Tuchel.
‘I think the game was exceptional, the first time we are here.’
MORE : West Brom demand £20m for Manchester United target Sam Johnstone