Park's countryman Jamie Donaldson is alone in second place after an opening- round 65 at Fuerteventura Golf Club.
Roger Chapman and Christian Cevaer share third place at 4-under-par 66.
Park flew out of the gate on Thursday with a pair of birdies in his first three holes. He closed his front nine with a birdie, then chipped in for birdie at the 10th.
He added birdies at 13 and 17 to vault ahead of Donaldson on the leaderboard.
Park burst on to the scene on the European Tour in 1999. He lost in a playoff in his first start then won his second, the European Grand Prix. Park has not visited the winner's circle since but has recorded top-10s in his last two starts, including a tie for fifth at last week's Open de Sevilla.
'It was a little difficult to deal with because to win was obviously a goal of mine but it came a bit quicker than I had envisioned so it was a bit of a shock to the system,' said Park. 'I didn't really improve for a while. There were a couple of years where I stagnated a bit in all aspects of my game while every one else improved. But I have improved over the last few years so I am just trying to continue to do that.'
Donaldson began on the second nine and promptly bogeyed his first hole. He also bogeyed his 12th hole but mixed seven birdies in his round to be within one of the lead.
While Park won early in his career, Donaldson is still looking for win No. 1. He posted his highest finish on the Order of Merit last year, 58th, and has definitely seen improvement.
'This is my third full season and I have been improving every year,' said Donaldson. 'I have been working on my swing hard in the winter but it takes a little bit of time for everything to sink in. Hopefully this week it will sink in nicely.'
Diego Borrego, Matthew Cort, Ricardo Gonzalez, David Lynn, Miguel Angel Martin, Jean-Francois Remesy, Jarmo Sandelin and Marcel Siem are knotted in fifth place at minus-3.
Spain's Jose Maria Olazabal opened with a 1-over-par 71.
'I didn't hit the ball too badly from tee to green but when it doesn't go in the hole it makes it difficult,' said the two-time Masters champion. 'I just need to hole a couple of good putts and things might change for me.'
Olazabal is one stroke ahead of defending champion Kenneth Ferrie, who carded a 72 on Thursday.