Not a bad way to start your professional career.
Quiros, a 22-year-old rookie playing for the first time with a European Tour card, closed with a skillful 5-under 67 to overtake third-round leader and native South African Charl Schwartzel.
He finished at 13-under-par 275 and became the first non-South African to win the Dunhill Championship in three seasons.
'I can't imagine that I...won this tournament. It is impossible for me,' said Quiros, who had played three previous European Tour events on invitation.
Schwartzel, the winner two seasons ago, held a two-shot lead overnight but managed only an even-par 72 on Sunday. He had birdies at 15 and 16 to tie a surging Quiros, but found a water hazard at the 18th and ended at 12-under 276 for the championship.
England's Lee Westwood shot a 73 and finished a distant third at 9-under 279.
Schwartzel was leading by two shots even after a bogey at No. 4. But two more bogeys around the turn cost him sole possession of the lead, dropping him into a tie with Quiros and Westwood at 10 under par.
That's when Quiros made his move.
With three straight birdies beginning at No. 13, the young Spaniard built a two-shot lead on Schwartzel. Playing two groups behind the new leader, Schwartzel forged a tie at 12 under when he birdied the 15th and 16th.
But Quiros finished with a birdie at the par-5 18th for the second day in a row to make himself the leader again.
He could have played it safe, taken a routine par and waited Schwartzel out -- play conservatively, friends told him -- but Quiros decided to go for the birdie.
Schwartzel was unable to match him, closing with consecutive pars to finish one back. He found the water with his second shot at the 18th.
'I had a lot of luck, so I have to be happy,' Quiros described his back nine and the outcome.
'Now I'm king for the week,' he said.
South Africa's Darren Fichardt had a 69 and tied for fourth place with England's Ross Fisher (70) at 8-under 280. Hennie Otto (72), also of South Africa, and Welshman Mark Pilkington (75) were a shot further back at 281.
Star South African Ernie Els, who won his fourth Dunhill crown last season, closed with a second-consecutive 69 and shared eighth place with Scotland's Alan McLean (67) and Italy's Alessandro Tadini (69) at 6-under 282.