Bjorn led overnight and finished at 14-under 279 to earn his first win since the Estoril Open in Portugal last year. He had three birdies in the final round, including one on No. 18 to capture his 11th European Tour title.
Quiros closed within two shots of the lead with a birdie on the 14th, but faltered at the end, bogeying two of the final four holes, including a three-putt on 15.
World No. 2 Martin Kaymer shot 71 to finish 2 under in a tie for 28th. He needed to finish at least second to overtake Lee Westwood for the top ranking.
The 134th-ranked Bjorn led Markus Brier by one shot entering the final round and said it was a question of "hanging in there" on the final day.
"I played solid golf. I think I made one bogey in the last 54 holes. On this golf course and in these conditions, that's good going," Bjorn said, referring to Thursday's high winds that made the course almost unplayable.
Bjorn, 39, added that the win was made all the more special because the field included players such as Westwood, who didn't make the cut, and seventh-ranked Steve Stricker, who finished 1 over in a tie for 45th.
"Well, the field this week was unbelievably strong, and you know, that shows where European Tour golf is at the moment," Bjorn said. "We have got a lot of players up there in the top 10 and a lot of them played this week. You know, that gives you a few extra points."
LADIES EUROPEAN TOUR: In Melbourne, Australia, Yani Tseng successfully defended her Women's Australian Open title, shooting a final-round 2-under-par 71 to win by seven strokes.
Tseng finished with a four-round total of 16-under-par 276 on the par-73 Commonwealth Golf Club course.
No. 1-ranked Jiyai Shin was tied for second with two others. Shin shot a final-round 74, level with Ji Eun-hee (74), and Melissa Reid, who shot 68.
Four-time champion Karrie Webb shot 70 and finished 11 behind Tseng. Laura Davies shot 74 and finished at 290, 14 strokes behind the winner.