The 44 year old birdied three of his last six holes to take a two shot lead over Spaniard Alvaro Velasco at Pula.
Winner of last year's Mercedes-Benz Championship, Kingston has just returned to Europe after taking a two-month break and his only mistake came with a bogey at the 413 yard third, his 12th.
“We played in perfect conditions,” said Kingston. “The course is great. It’s tricky, and with this wind it can become complicated.
“It’s a challenging course with tough tee shots, and it’s difficult to get the ball close to the hole.
“I kept the ball in play nicely off the tee and rolled it nicely. I have been playing decently lately, but still not well enough.”
Velasco had five birdies, but also dropped two shots.
“It was a good round,” he said. “I played very well, particularly the back nine. I started holing some putts.
“Putting has been the key of my game - I also holed a 25 metre birdie chip on the sixth.
“It doesn’t seem to be a hard course, the rough is light, but there aren’t many birdie holes.”
Bristol's Chris Wood, fifth and third in the last two Open Championships, returned a two under 68 to be in joint third place with Frenchman Raphaël Jacquelin and Ireland's Gary Murphy, who had to return to The European Tour Qualifying School last November to regain his card.
Ryder Cup Dane Søren Hansen, the highest ranked player in the event, stood one over on his return to action for the first time since last month's Masters Tournament.