SHANGHAI (REUTERS) - Dustin Johnson threatened to run away with the WGC-HSBC Champions tournament before a double bogey at the final hole of his third round today gave a glimmer of hope to the field.

He pushed his tee shot into the water at the par-five 18th - which followed an earlier double bogey - yet he still managed a six-under-par 66 in perfect scoring conditions to lead England's Ian Poulter (63), the defending champion, by three.

Soft greens and the absence of a breeze led to a birdie blitz and also a deteriorating air quality as a moderate smog hung over Sheshan International.

But Johnson was more bothered by his tardy finish than the smoky air, despite posting an impressive 18-under 198 total with one round left.

"I'm still a little mad from my double bogey at 18 but, obviously, a three-shot lead going into Sunday is good," the seven-time PGA Tour winner said.

Poulter vaulted into second place on 15-under, with Northern Irishman Graeme McDowell (64) another shot behind.

McDowell's compatriot Rory McIlroy (67), Englishman Justin Rose (65) and Canadian Graham DeLaet (65) are six strokes back of Johnson in a tie for fourth.