CSKA, Petrov's first club, beat third from bottom Vidima-Rakovski Sevlievo 1-0 to move on to 54 points from 22 matches. Second-placed Chernomorets Burga visit Slavia Sofia on Monday.
The crowd applauded in the 19th minute in Sevlievo to commemorate Petrov's shirt number at his English Premier League club Aston Villa.
All the teams in Bulgaria expressed their support for the player in various ways at their weekend matches.
CSKA and Vidima-Rakovski players wore T-shirts sporting his name and with the message "We are with you" during the warmup.
Petrov, 32, played for CSKA between 1996-99 and was instrumental in helping the Reds win the league in 1997 and the Bulgarian Cup in 1997 and 1999.
CSKA, 31-times champions, are chasing their first league title since 2008.