Westwood was three shots behind Rory McIlroy and Thomas Bjorn when the day started, but finished it with a one-stroke edge over playing partners Stephen Gallacher and Marcel Siem, as well as first-round leader Rafael Cabrera-Bello.
Gallacher and Siem each carded four-under 68s at the Emirates Golf Club, while Cabrera-Bello managed a two-under 70.
McIlroy is two shots back at 13-under after an even-par 72 on Saturday. He is joined there by Martin Kaymer, Scott Jamieson and Joel Sjoholm. Kaymer and Jamieson each shot rounds of two-under 70, while Sjoholm had the low round of the day with a six-under 66.
Bjorn stumbled to a one-over 73 and is tied for ninth at minus-12 with Ben Curtis and George Coetzee.
Westwood was coming off a seven-under 65 on Friday that concluded with three straight birdies. He added three birdies on his first four holes Saturday to reach 13-under.
"I got off to a very good start, three under after four, rolled the ball well on the greens and hit a lot of good quality iron shots," the world No. 3 said Saturday.
Westwood sandwiched a pair of birdies around a bogey late in his opening nine and made the turn at 12-under, then put together three more birdies over his first four holes on the back side and closed the round with five pars.
"I played nicely again," the Englishman added, "very solid."
Westwood has 21 career European Tour victories and has had a decent start to 2012 with a tie for 17th at Abu Dhabi and a tie for 12th at the Qatar Masters.
"I've won 30-odd times in my career," stated Westwood, who has also won two PGA Tour events and 10 other times around the world. "So I'm used to knowing what to do when I'm leading a tournament."
McIlroy, the second-ranked player in the world and the 2009 Dubai champ, had a birdie and a bogey on an uneventful front nine, then bogeyed the par-five 10th to start an up-and-down back. He added two more bogeys and three birdies over the final eight holes.
Bjorn, the 2001 Dubai winner, held a two-shot lead at 15-under after a birdie at the 10th, but bogeyed three of his last four holes.
NOTES: Defending champion Alvaro Quiros managed a one-under 71 Saturday and is tied for 35th at minus-five...Paul Lawrie, last week's winner in Qatar, is six-under par, as is American John Daly...Colin Montgomerie is one-over par after struggling to a five-over 77 Saturday.