'I was really committed to come here and try to win, unless I win a WGC event or a major, I only have a few chances to win in Europe, and to be able to do it in Spain makes it even sweeter,' said Garcia. 'I'm happy here with my people and it's a wonderful feeling to come through like I did and play the last 13 holes in 5 under par.'
Simon Khan, who held a piece of the lead after the second and third rounds, carded a 1-over 71 to take second place at 8-under-par 272. Carlos Rodiles was one stroke further back at minus-7 after a closing 69. Markus Brier, Francois Delamontagne and Santiago Luna shared fourth place at 5-under-par 275.
Garcia quickly fell behind Khan, who birdied the first. Garcia bogeyed the first and second to drop back to minus-7 and parred the next three holes at Pula Golf Club.
The Spaniard then birdied the par-5 sixth for the fourth straight round. Garcia birdied the seventh to get back to 9 under but dropped a shot at eight. He responded with a birdie at the ninth to take the lead for good from Khan, who had fallen back to minus-8.
Garcia moved to 10 under with a birdie at the 11th and picked up another stroke when he birdied the 13th. The 24-year-old collected his final birdie at the 16th and parred the final two holes for the four-shot victory.
'I don't know why my head wasn't in the right place at the beginning, I was a bit tentative and Simon started well, which put a little bit of pressure on me,' said Garcia. 'Getting up-and-down for par on the third and fourth was huge for me to keep me in the right mood and after that I started loosening up and made a few birdies.'
Khan had moved two shots clear of the field with his birdie at the first. However, the Englishman stumbled to back-to-back bogeys from the third to fall back to the field.
The 32-year-old Khan birdied the seventh, but faltered to a bogey at the next. He tripped to another bogey at the 11th. Khan atoned for that error with a birdie on No. 13 and closed with five straight pars to take second.
'That was the key,' said Khan, of his bogey at 11, a hole Garcia birdied. 'The second shot jumped on me and I had no shot from over the green. But to be fair Sergio showed his class and just when he needed to, he produced the shots at the right time.'
Paul Broadhurst posted a 3-under 67 to finish at 4-under-par 276. He was joined in a tie for seventh by Alastair Forsyth (68) and Gonzalo Fernandez-Castano (71) at 4-under-par 276. Jose Maria Olazabal, the 2003 runner-up, finished one stroke further back at minus-3.