Englishman David Howell and Spaniard Miguel Angel Jimenez each carded rounds of 5-under-par 67 to share second place. Sam Osborne and Jarrod Lyle were one stroke further back at minus-4.
Els began his day on the front nine of the Majlis Course at Emirates Golf Club. After a pair of pars, the South African birdied the par-5 third to get into red figures.
The world's No. 3 player poured in a birdie putt at the eighth and made it two straight as he birdied No. 9 to make the turn at minus-3.
Els' back nine was very similar. He birdied the par-5 13th to get within one stroke of the lead. Els, who won this event in 1994 and 2002, rolled in a birdie try at the 17th to grab a share of the lead. He grabbed the outright lead with a birdie at the last.
'I had a nice time out there,' said Els, the only two-time winner of this event. 'I found my feet on the back nine and was very aggressive. I was hitting driver on just about every hole and although I didn't hit many fairways, it felt solid. All in all it was a good day's work and I'm pleased with 66. That was a good score today.'
Howell, who won the title in 1999, got off to a quick start with birdies at the second and fifth. However, he faltered to a bogey at the par-4 eighth. The Englishman bounced back with an eagle at the par-5 10th.
The 29-year-old stumbled to another bogey at the 11th to drop back to minus-2. Howell converted consecutive birdie putts from the 13th and moved to 5 under with a birdie at 16. He closed with two pars to share second place.
'I've been playing dreadfully,' said Howell, who has played in the United States the last few weeks. 'My game deteriorated like the weather over the three weeks out there, but the greens are great here and everything is nice, familiar territory. I went back to a few old drills and all in all played quite nicely.'
Jimenez, who is coming off a second-round loss to Chad Campbell at the WGC- Accenture Match Play championship, got off to a slow start with just one birdie over his opening nine holes.
The Spaniard caught fire around the turn though. Jimenez drained a birdie try at the 10th and made it two in a row as his birdie putt at 11 found the bottom of the cup.
Jimenez moved to minus-4 with a birdie at the 13th. He got to 5 under with a birdie at the par-4 16th before closing with a pair of pars.
Thomas Bjorn, the 2001 winner here, posted a 3-under-par 69. He was joined in a tie for sixth place by Robert Karlsson, James Kingston, Andrew Marshall, Charl Schwartzel, Henrik Stenson, Nick Dougherty, Peter Fowler, Pierre Fulke and Peter Hedblom.
Mark O'Meara, the defending champion, got off to a rough start as he carded a 1-over-par 73. He posted two birdies and three bogeys and stands in a tie for 76th.