Kompany lost his first match as player-director of Anderlecht
The center-back named himself in the beginning XI yet could do nothing to stop a late winner in a 2-1 defeat at home by KV Oostende.
Michel Vlap gave Anderlecht the lead yet Ronald Vargas and Fashion Sakala scored in every half for Oostende.
It was Kompany's first game since leaving Man City in May.
Kompany scored five goals in 73 appearances for Anderlecht from 2003 to 2006, helping them to win two league titles.
A banner of Kompany, who played the full an hour and a half, with the message "left like a prince, returned like a king!" was held up in one of the stands.
There was additionally an energizing speech from the previous player Tomasz Radzinski, who had spells at Everton and Fulham, on the pitch before the match.
Previous Manchester City midfielder Samir Nasri went ahead as a substitute for Anderlecht, while 22-year-old City loanee Philippe Sandler was likewise named in the squad.