Marcelinho, born in a small town in the Amazon region of Brazil and making his first international appearance at the age of 31, struck in the 20th minute of a game almost totally dominated by Portugal.
The hosts were repeatedly foiled by Bulgaria goalkeeper Vladislav Stoyanov who capped an outstanding display by diving to his right to save Ronaldo's penalty, awarded for handball, in the 69th minute.
Ronaldo, who has missed three penalties this season for Real Madrid, also turned the rebound wide.
His unhappy night began when he fired over with the goal at his mercy from an unmarked position in the seventh minute.
The former FIFA World Player of the Year also had four attempts at goal from long-range free kicks, two hitting the wall and the others forcing saves from Stoyanov.
The visiting keeper made six stops in the first 10 minutes alone, including one excellent effort denying Nani, as Portugal threatened a goal spree.
Bulgaria then went in front when Marcelinho, who qualified for them after spending five years with Ludogorets Razgrad, forced his way past two defenders and poked the ball past Anthony Lopes.
After that the game became predictable as Portugal poured forward and played plenty of neat football around the Bulgaria area but either lacked the killer pass or were foiled by Stoyanov.
The goalkeeper completed his evening's work by making a superb stop to turn away a close-range header by a frustrated Ronaldo with five minutes left.
"We are not satisfied with the result. We started brilliantly, in the first 15 minutes, we were strong, consistent, the goalkeeper make some fantastic saves and then we lost some concentration," said Portugal coach Fernando Santos.
(Writing by Brian Homewood; Editing by Tony Jimenez)
