By Simon Evans

MIAMI (Reuters) - South African duo Ernie Els and Charl Schwartzel head into Sunday's final round of the WGC-CA Championship at Doral tied for the lead on 12-under par, one stroke ahead of Ireland's Padraig Harrington.

The 25-year-old Schwartzel produced a five-under 67 in the breezy sunshine of the Blue Monster course on Saturday while Els, the overnight leader, had some ups and downs in his round of 70.

Els, who has not won on tour in two years, will now play the final round with a compatriot 15 years his junior and who he hosted while Schwartzel practiced last week.

Schwartzel, who won two early events on the European Tour this year, will go head-to-head with a player who his father once partnered and despite his admiration of Els, who won this competition when it was held in Ireland in 2004, Schwartzel said he was only focusing on winning the title on Sunday.

"When you are out on the course it is every man for himself. I am sure we'll have a good time and a good battle," he said.

Els continues to look confident but missed a three foot birdie putt on the 16th, having earlier missed from four feet on the 13th to bogey.

"I felt a little uncomfortable on those shorter putts today. I think it could have been the breeze," said Els.

"I'm six foot four (1.93m) and I move around a little bit, or it feels like it. I think it was a bit of a weak point today and it cost me a little bit."

Harrington would also have had a share of the lead had he not three putted the 18th to end a fine round with a bogey.

The Dubliner made six birdies in his five-under 67 round that was faultless until the final hole, but he remains in strong contention for Sunday along with Australian Robert Allenby (71) who is two shots off the lead.

"It leaves a sour taste to bogey the last but finishing 11-under or 12-under has no real effect on the outcome tomorrow. There are three of us up there, whoever plays the best golf is going to win the tournament," said the Irishman.

German Martin Kaymer produced the day's top round with a six-under 66 moving him into sixth place on eight under, one shot ahead of Fijian Vijay Singh (70), Dane Soren Hansen (71), Britain's Paul Casey (68)and American Matt Kuchar (67).

Phil Mickelson, the world number three and defending champion, hit five birdies and five bogeys in his even-par round and ended up in some pain after jarring his elbow playing his second stroke on the 18th.

(Editing by Greg Stutchbury)