THIRD ROUND LEADERBOARD:
-10 E Els (SA), -9 B Curtis (US) Selected others:-4 R Goosen (SA), J Furyk, Davis Love III, B Weekley (All US) -2 P Mickelson (US) -1 C Montgomerie (Sco) +4 B Davis (Eng)
Prior to the WGC-CA Championship, Els had not won a tour event two years
Ernie Els took a one-shot lead at the Arnold Palmer Invitational after joint overnight leader Ben Curtis carded two late bogeys on day three.
The American dropped shots on the par-five 16th and the par-four 17th to finish with 70, one shot behind Els.
South African Els finished the day three under following a round of 69, helped by birdies on the 12th and 16th.
American Chris Couch is two shots behind Curtis while Colin Montgomerie is a further five shots adrift.
The Briton finished the day on 71 to follow his first and second round scores of 72 and 71 at the Bay Hill course in Orlando.
Kevin Na, who had been one shot behind the overnight leaders alongside Phil Mickelson on six under, dropped off the pace following a round of 72, two shots behind Italian Edoardo Molinari, who trails Els by four strokes.
Couch enjoyed his share of fortune on the last hole.
His ball bounced off three rocks on the edge of greenside water before landing on to the green, allowing him to make par.
"I kept thinking, 'Please, please, bounce on the green, baby, bounce on the green,'" said Couch.
"I've never considered myself a very lucky person on the golf course but that was a great break at the right time."
World number three Mickelson suffered a poor day with the putter, carding five bogeys to trail Els by seven.
"There's a lot of work left," said Els, who won the WGC-CA Championship earlier this month.
"Obviously, I'm still in a very good position. I would have taken it before the tournament started.
"I would like to keep working and just try and concentrate on playing good golf on Sunday."