Lee Westwood is one back after dropping his only shot of the day at the last.
Order of Merit leader Henrik Stenson and second placed Danny Willett are tied for 17th on three under.
Rory McIlroy, bidding to win the European Tour's season finale in Dubai for a third time, posted six birdies in a 68 but is eight shots adrift.
The Northern Irishman, who has never finished worse than 11th in seven appearances at Jumeirah Golf Estates, had opened with a three-over 75, his first over-par score in the event.
"Yesterday was just one of those days. I was mentally very flat, still in holiday mode, and not quite switched on to what I needed to do," he said.
"If can keep improving each and every day, then I might not be too far away at the end of the week."
The Tour Championship is the final event of the Race to Dubai, with four players still in with a chance of topping the money list.
Open champion Stenson, who won this tournament with a course-record 25 under total at the Earth Course in 2013, leads by 299,675 points but Masters champion Willett can leapfrog the Swede should he win the tournament.
Willett would also top the list if he finishes second and neither Stenson nor Alex Noren win in Dubai.
Noren, another Swede, needs to finish at least second and hope Stenson and Willett finish down the field and he is five strokes off the lead after a round of 69.
Stenson, the 2013 Race to Dubai winner, was more concerned with the well-being of a female spectator hit on the head by his tee shot on the 13th.
"I had some reports later in the round that she was doing OK. I'm just making sure that we're going to get her details so I can send her something nice," he said.
McIlroy, who has won the Race to Dubai for the last two years, has an outside chance which requires several permutations falling into place - including Stenson finishing no higher than 46th in the 60-man field.

Twelve homes were evacuated after the hole opened in Ripon, North Yorkshire, at 22:30 GMT on Wednesday.
The hole measured about 20m (66ft) by 10m (33ft) and 9m (30ft) deep.
The BGS said Ripon lies in one of the most susceptible areas of the UK for sinkholes because of its "Permian gypsum deposits".
It said these can dissolve more quickly than surrounding limestone, leading to the enlargement of underground caves.
Experts are still examining data from the site behind the houses in Magdalen's Road but, releasing its initial findings, the BGS said sinkholes were often caused by surface water penetrating the ground, or fluctuations in groundwater levels.
In 2014, a 100-year-old detached house in an adjoining street was demolished after a 25ft-wide (8m) sinkhole opened.
According to the report, the wider area of Ripon periodically encounters sinkholes and in the 1980s and 1990s a hole was appearing every two to three years.
No-one was injured in the latest collapse with the back gardens of two properties the worst affected.
A sewerage system connected to several of the properties on the terrace fell in as the hole appeared.
One resident described seeing the ground moving and finding her steps leading into the garden had gone.
On Friday, further cracks appeared in the ground and on walls at the site.
Ben Cairns, North Yorkshire Fire Service station manager, said: "Our main concern at the moment is what impact the weather is going to have for the next few days."
The BGS is continuing to analyse data from the site.
Sergio Garcia and Francesco Molinari both carded five-under 67s to share the lead at nine under at the halfway stage of the DP World Tour Championship.
[NEXT_CONCEPT]
A large hole that appeared behind a row of houses was in one of the UK's most susceptible areas for sinkholes, the British Geological Survey has said.