Starting at the 10th, Harrington began moving in the right direction with an eagle at the 13th before picking up birdies at the 15th and 16th to quickly climb to four under par.

A bogey at the next checked his progress but it proved a minor setback as Harrington responded with four birdies on the front nine to complete a satisfying opening effort.

"It's always nice when you come back to defend a title to put in a good showing. It's great to be up near the top of the leaderboard, even though it's early days, and it's even nicer to be playing well. So it's a case of so far, so good," he told the European Tour website.

"I left a few shots out there but I'm still very happy with the score. I'm a bit surprised the scoring in general isn't a little lower than it is.

"In our group, we must've made at least 25 birdies between us, and in some ways we fed off each other. A lot of times we made similar sorts of birdies on the same holes, which definitely helps you to keep your own momentum going."

Luiten, meanwhile, carded the best round of the day so far with a 63 as the par-71 layout in Johor Bahru gave up a number of low scores.

Luiten's bogey-free round was built around four consecutive birdies from the 15th with the Dutchman collecting eight in total to set the clubhouse lead on eight-under.

"If you make birdies on the par fives, which are all reachable today, then you've only got to find four more birdies somewhere else and make no bogeys for a 63 and that's what I did," he said.

"On this course, you can really attack the pins, especially as you've got a lot of wedges in your hand. I found most of the fairways off the tee and that put me in a great position to make some birdies.

"I think a few guys will go very low this week, depending on the weather. I think a 61 or 62 is very possible, if you get your putter going. If you look at previous years, the winning score has been around minus 20 or so. So that tells you what's possible on this course."

Frenchman Gregory Bourdy and Australia's Marcus Fraser joined Harrington on seven-under as they also returned 64s while Englishman James Morrison, fresh from his eighth place in Singapore, continued his good form as a 66 that featured six birdies and a bogey saw the 26-year-old also in the mix at five-under alongside Charlie Wi and Nicolas Meitinger.

Henrik Stenson was four under par following an opening 67 while Scottish duo Richie Ramsay and Stephen Gallacher were at three-under.