Fonseca had promised to dress up as the masked vigilante if Shakhtar reached the knockout stages and the Portuguese coach kept his promise after the match.
"This is the most joyful press conference of my career," the 44-year-old told reporters.
"Tonight we played an almost ideal game. We were very disciplined in defence and broke through to attack very effectively.
"It was very important to close up some particular zones for Manchester City where they are usually very dangerous. I think we did that well and they did not threaten as they normally would."
Man City had not lost in any competition since an extra-time defeat to Arsenal in last season's FA Cup semi-final prior to the loss at the Metalist Stadium.