The standout performer for the Bavarians this season was heavily linked with a switch to Stamford Bridge earlier this year, publicly voicing his admiration for Chelsea boss Jose Mourinho.
However, the former Shakhtar Donetsk star has revealed it did not take him long to make up his mind when the Bundesliga champions joined the race for his signature.
"Chelsea also wanted to sign me. They were seriously interested and made great efforts," Douglas Costa told Bild.
"But I really only wanted to work with Guardiola and join Bayern.
"I made a conscious decision to join Bayern because of the presence of Guardiola. I was convinced that I would learn more at Bayern under Guardiola."
The 25-year-old has developed into a key figure at the Allianz Arena, scoring twice and setting up seven more in 12 Bundesliga appearances for die Roten so far.