Javier Pastore had given the visitors the perfect start at Stade Louis II with his first Ligue 1 goal of the season in the eighth minute, the Argentinian meeting a deflected header from Alex to head past Danijel Subasic from close range.
Zlatan Ibrahimovic had three good chances saved by the Monaco goalkeeper, but the champions still looked on course to secure victory until Thiago Silva's 74th-minute own goal.
Blanc felt that his side had done more than enough to take all three points on Sunday, but his captain's late own error meant that they had to settle for a point.
"The first half was better controlled, but after it was a bit more complicated," said Blanc.
"We came to win, and dominated the first half. We thought we could win.
"The (own) goal is a bit unfortunate."
The result sees PSG remain five points clear at the top of the table.
