Oosthuizen, the 2010 British Open winner, played a bogey-free round with seven birdies, while Scott finished his round with two birdies and an eagle on the par-5 ninth hole.
Both Oosthuizen and Scott took advantage of the pristine conditions and the five par-5 holes on the Jose Maria Olazabal-designed course at Mission Hills. Oosthuizen birdied all five, while Scott had four birdies to go along with his eagle.
''It was a solid day that all of a sudden turned into a really good day,'' Scott said. ''With five par-5s, it kind of sets up well for my game and the plan is to just take advantage of the 5s and hopefully hang in there with the leaders all week.''
The Australian, ranked sixth in the world, is still looking for his first tournament win of the year. He nearly captured his first major at the British Open in July before blowing a four-shot lead over Ernie Els with four holes to play.
His best finish since that collapse was a tie for sixth place at the BMW Championship in September.
Oosthuizen also said the key to his game was hitting solidly off the tee on the par-5s, something he'll need to do all week if he's going to stay atop the leaderboard.
''If I can keep doing what I'm doing on the par-5s, you know, hitting the fairways and leaving myself with the irons or a 5-wood or something, you've got a good chance,'' Oosthuizen said.
Hanson backed up his big win at the BMW Masters in Shanghai last weekend with a superb opening round in Shenzhen, making seven birdies against one bogey.
The Swede is second on the European money list, within striking distance of leader Rory McIlroy. If Hanson wins the $1.2 million paycheck at Mission Hills this weekend, he will overtake McIlroy with only four events left on the calendar.
''It's nice to get off to a good start, of course, coming off last week. You try to save a bit of energy the last couple of days and try to be ready for today,'' Hanson said. ''I've been on the road now for three or four weeks. Just need to keep your head fresh and this is a very demanding golf course. You can make some easy mistakes around here,'' he said.
Mickelson was further off the pace before sinking a 25-foot putt for eagle on the same hole as Scott – the par-5 ninth – to finish off his round of 66.
''It was a great way to finish with an eagle. I was hoping just to make birdie on the last hole,'' Mickelson said. ''I think the reason I was so calm today was I drove the ball extremely well and hit every fairway.''
Lowry, meanwhile, stuttered down the stretch. After making birdies on the 15th and 16th holes to take a two-stroke lead over the field, the Irishman had bogeys on his final two holes – missing near-identical 10-foot putts – to drop him back into a tie for third.
''Felt like I had the ball on a string all day and felt like it came very easy to me today,'' Lowry said. ''Just to bogey those last two was disappointing.''
Dustin Johnson shot a 67 to sit two strokes off the lead with Thailand's Prom Meesawat.