The Tottenham winger struck the decisive blow in the dying embers of the opening half, receiving the ball from Adam Matthews to cut in from the right and send a deflected shot beyond Nikolay Mihaylov in the Bulgaria goal.
Bale also lashed a thunderous first-time volley against the bar after linking superbly with captain Aaron Ramsey.
The duo and Swansea midfielder Joe Allen were again the outstanding performers for Gary Speed's side, who are almost unrecognisable from the squad that began this group with four straight defeats as they ended their Euro 2012 campaign on a high.
The game was played in a surreal atmosphere as only small pockets of Bulgaria fans chose to attend the Vasil Levski Stadium following a poor run that now extends to seven games without a win.
Ivelin Popov wasted their best chances as Wales controlled the majority of the contest.
Speed had been able to name an unchanged side from the 2-0 win over Switzerland, making it the first time Wales had fielded the same XI since their Euro 2004 play-off fixtures against Russia.
Bulgaria caretaker boss Mihail Madanski, by contrast, had made six changes from their friendly defeat to Ukraine.
And Wales' confidence from their recent revival in form and settled squad was clear to see as they carved out early chances.
Craig Bellamy could have given them a fifth-minute lead after Georgi Terziev failed to cut out a Ramsey pass, but the Liverpool striker fired straight at Mihaylov.
Bale tricked his way past three defenders but could only get away a tame shot away under pressure from Ivan Ivanov, before the Spurs star's pull-back was cleared by Stanislav Manolev with Bellamy lurking.
But Wales were also guilty of some needless defensive lapses, and a poor mistake in possession by Darcy Blake gave Popov a chance, but the striker dallied and Neil Taylor cut out the danger.
Bale's pace then left Petar Zanev for dead down the right but Bellamy opted not to take on the shot from the deep right-footed cross.
Bulgaria continued to sporadically threaten and Popov ought to have done better when he fired across the face of goal after a wonderful flick from the lively Valeri Domovchiyski.
Speed was forced into a defensive reshuffle after 41 minutes as he lost Blake to a calf injury, with Celtic's Matthews coming on as his replacement and Chris Gunter moving to centre-half.
But Wales made light of that blow as Bale was found by the substitute before cutting in onto his left foot and shooting low into the net with the aid of a deflection.
Bellamy failed to take another fine chance early in the second half after lovely build-up by Bale and Ramsey, firing high over the bar from the edge of the box.
The veteran forward was again involved moments later, curling narrowly wide after driving in off his flank.
Wales and Bale then went close to a spectacular second in the 59th minute. Ramsey juggled the ball on the edge of the box and flicked the ball over his shoulder for the winger to smash a first-time volley against the underside of the bar with Mihaylov beaten.
The hosts hit back with their first concerted pressure but two blocked shots from captain Stiliyan Petrov were the best they could manage.
Ramsey fired over on 76 minutes, but it did not matter as Wales closed out the game despite some nervy moments.