Rumford collected his first European Tour win in 5 1/2 years last week in South Korea and is bidding to become the first winner of consecutive tournaments on the tour since Braden Grace in January 2012.
Rumford's round Saturday included a string of birdies over No. 6-8 and 15 pars as he moved to 12-under 204 for the tournament.
Second-round leader Mikko Ilonen was 1-over 73 Saturday and dropped to 11-under for the tournament while Pablo Larrazabal (69 Saturday) is in third at 10-under and Kiradech Aphibarnrat (72) is fourth, three strokes off Rumford's lead.
While Rumford was a picture of consistency -- he made putts of 1 foot, 2 feet and 10 feet for his birdies -- Ilonen had problems Saturday. He had bogeys at Nos. 1 and 6 -- holes he birdied each of the first two rounds -- but answered with birdies at 2 and 7. He was even through the day until the final hole, where a poor drive caused him to bogey the par-5, 630-yard 18th.
Larrazabal had four straight birdies in one stretch Saturday but also posted four bogeys and three other birdies in an up-and-down round. Aphibarnrat's even-par day included four birdies and four bogeys.