Thailand's Kiradech Aphibarnrat (66) was sharing third position with McIlroy on 201.
"The eagle on 13 was the spark that I needed to get myself up the leaderboard," Northern Irishman McIlroy told reporters at the $7-million European Tour event.
"I feel if I play the same way and execute a little bit better there is definitely a lower score out there for me.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"I've played very much within myself so if I can get something going and get some momentum out there tomorrow there is no reason why I can't go lower than that," added McIlroy.
"I'll be setting myself a target somewhere a little lower than 20-under and we'll see where we go from there."
European Ryder Cup player Dubuisson has had a mediocre season but is glad to be back at the Montgomerie Maxx in south-west Turkey.
"This is a course that I feel great on," said the Frenchman. "My long game has been really good since the beginning of the year but my short game was just really bad.
"I changed my putter about six weeks ago and it has been getting better and better since then so my game feels in good shape. I’m very excited about tomorrow."
(Writing by Tony Jimenez in London; editing by Clare Fallon)
