Brooks Koepka holds a one-shot lead from Gavin Green and Kiradech Aphibarnrat after the opening round of the WGC-HSBC Champions, while Hideki Matsuyama got his defence off to a woeful start.
The U.S. Open champion recorded back-to-back birdies before a putt from the fringe salvaged par on the ninth, keeping his advantage at eight-under intact.
Koepka hit the turn in 31 after registering an eagle on the par-five 18th when he rolled the ball in from 21 feet, and a bogey on the third was the only blemish on a solid day.
Green produced a bogey-free round to put himself in contention, a birdie at the last sending him level with Aphibarnrat – who enjoyed a run of seven successive birdies from the 16th to the fourth – after a seven-under 65.
Matsuyama is bidding to become just the third man after Tiger Woods and Dustin Johnson to win back-to-back WGC events, but a mixed return left him 10 strokes back.
A triple-bogey seven at the par-four third proved damaging, while he dropped a shot on his final hole after successive birdies had moved him to one over.
Inconsistencies plagued Haydn Porteous' round. The South African sunk a whopping 10 birdies but a double-bogey seven at the 14th and dropped shots on four and nine left him in a tie for fourth with Patrick Reed.
Last year's runner-up Henrik Stenson and world number one Johnson carded four-under 68s, while Jason Day is one behind the duo in a share of 21st.