Charl Schwartzel held off the strong challenge of Ricardo Gonzalez to post a five-under-par 66 and take a one-shot lead into the final day at the Madrid Masters.
The South African streaked ahead early on - leaving Marcus Fraser, with whom he shared an overnight lead, and Robert Rock in his wake.
But five groups ahead, Gonzalez burst into life on the back nine - firing six birdies and an eagle for a nine-under-par 62 which took him to 13 under for the tournament.
He could have been the outright leader, but Schwartzel fended him off by holing a tricky putt for par on the 17th before sinking a 10-footer for birdie at the last to snatch a one-shot advantage on 14 under.
Spaniard Pablo Larrazabal equalled Gonzalez's score, racking up six birdies on the back nine to move to third place on 11 under. Three players - Englishman Paul Waring, Andrew Tampion and Carlos Del Moral - are 10 under.
Schwartzel, 24, said he considered pulling out Friday morning because of illness and a sore shoulder - and despite still not feeling 100%, he raced ahead with birdies at four, five and eight and an eagle at seven.
He wavered slightly around the turn, dropping shots at nine and 12, but birdied the par-five 14th and par-four 18th to steal a march on Gonzalez.
"I didn't feel very strong this morning but I felt I ground it out nicely today," said Schwartzel, who carded 69 and 64 in his first two rounds.
"I felt very weak and slept very badly last night but I felt better and better as the day progressed.
"Thankfully my shoulder is fine now after the physio treated it last night, but I still felt ill and got some medication from the doctor."
Asked if he may feel under pressure tomorrow, knowing Gonzalez had shot such a low score, Schwartzel replied: "Sixty-two is a great score, and tomorrow we'll have a good battle.
"I will try to do the same as the last three days and stick to my game plan. I'm hitting the ball well and I'm confident in my swing.
"I've got a good chance tomorrow."
Gonzalez, 38, was still struggling to take in his whirlwind back nine which put him in strong contention.
"I was one under after nine and thought to myself 'I need a few more birdies' - but to shoot nine under is unbelievable," he said.
"The key, I think, was my drive on 10. From there, I felt more confident. My putting was also very good on the last seven or eight holes.
"Spain is like a second home, and I feel very good here. I'll feel a little bit of pressure tomorrow but I'll try to make a good score again and play well.
"I will just play golf and enjoy it - that's the only thing I can do."
Waring is also a strong contender after a second four-under-par 67 followed a first-round 69, but joint overnight leader Fraser found it tougher going and could only manage a three-over 74 to leave him six under.
Miguel Angel Jimenez's chances of clinching the title which would take him to third in the European Tour Order of Merit look all but over - after a one-over 72 which meant he was 13 shots adrift of the lead, heading into the final day.
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