South African golfer Ernie Els was left shaking his head after the third round at the $US5 million ($A8.7 million) Mercedes Championship.

He shot an eight-under-par 65, matched the US PGA Tour 54-hole record score in relation to par, but still had only a slim lead with one round left at Maui's Kapalua course.

That's because KJ Choi compiled a course record 62 that included nine birdies and an eagle which left the chunky South Korean only two strokes behind Els.

Els was in complete control until he made a double bogey after pulling his tee shot into an unplayable lie at the 17th hole.

When Choi birdied the 18th minutes later, what had been a five-shot lead suddenly was cut to two.

Els had to settle for a 25-under 194 total, Choi was alone on 196, while South African Retief Goosen (66) was five strokes further back in third place.

"I'm still a little bit hot about 17," said the British Open champion.

"I made a bad swing (with a three-wood), tried to hit it a little too hard. I basically played the hole bad but other than that I did everything right.

"I hit a lot of fairways, a lot of greens. I had quite a fun day until 17. I think 25 under through three rounds is a personal best for me.

"The last two holes change it a little bit. I could have been leading by four or five shots. It makes me focus differently tomorrow. I can be aggressive."

The dogged Choi rose to prominence last year by winning twice on the tour and finishing 17th on the money list.

"I feel very confident about my swing right now," he said. "I started out well and as the round progressed I felt better and better."

Craig Parry, the only Australian in the 36-man field, was out of contention in 25th place, a distant 17 shots off the pace after a two-under 71.

After a frustrating second round with the putter, Parry again struggled on the greens: "It feels like the flat stick is the problem, but maybe I'm just not hitting it close enough," he said.

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