Oosthuizen, who won the British Open at St. Andrews two years ago, played bogey-free and birdied all five par 5s on the Jose Maria Olazabal-designed course. Scott, the runner-up at the British Open this summer, made four birdies and an eagle on the par 5s.
Two-time HSBC Champions winner Phil Mickelson was a stroke back along with Masters champion Bubba Watson, Shane Lowry of Ireland and Peter Hanson of Sweden, who can overtake Rory McIlroy on the European Tour money list with a victory in this World Golf Championship.
Oosthuizen and Scott are both looking for their first PGA Tour win this year, and the HSBC Champions would count toward that because both are tour members.
Dustin Johnson had a 67 and was two strokes behind, along with Prom Meesawat of Thailand.
Defending champion Martin Kaymer was in a group of seven tied for ninth at 68, along with England's Luke Donald and American Jason Dufner.
CHARLES SCHWAB CUP CHAMPIONSHIP
SCOTTSDALE, Ariz. (AP)—Defending champion Jay Don Blake birdied three of the final four holes for a 6-under 64 and the first-round lead in the Champions Tour's season-ending Charles Schwab Cup Championship.
The winner last year at TPC Harding Park in San Francisco, the 54-year-old Blake had a one-stroke lead over Gary Hallberg.
Fred Couples, Jay Haas, Olin Browne and Bill Glasson shot 66 on Desert Mountain's Cochise Course. Couples is playing for the first time since a back injury forced him to withdraw from the Boeing Classic in late August.
Schwab Cup points leader Bernhard Langer birdied the final two holes for a 69, Tom Lehman shot a 68, and Roger Chapman had a 69. Langer has a 211-point lead over Lehman and 657-point advantage over Chapman in the race for the $1 million annuity.
BANGKOK (AP)—One week after turning 14, Guan Tianlang of China had a 6-under 66 to build a two-shot lead after the opening round of the Asia-Pacific Amateur Championship.
Guan made eight birdies at Amata Spring Country Club to lead Daniel Pearce of New Zealand. Hideki Matsuyama of Japan, trying to win for the third straight year, was tied for 10th after opening with a 71.
The winner of the Asia-Pacific Amateur earns an exemption to the Masters and a spot in the final stage of qualifying for the British Open.
Guan won by 11 shots in his age division (11-12) last summer at the Junior World Golf Championships in San Diego. In April, he became the youngest player to compete on the European Tour at the China Open.