Graeme McDowell remains in pole position at the WGC-HSBC Champions in Shanghai - thanks to a little help from Masters champion Bubba Watson.

McDowell began the third round at Sheshan International with a three-shot lead over Ryder Cup team-mate Ian Poulter and four clear of Watson, but saw the American cut his deficit in half with three birdies in the first eight holes.

Watson picked up shots on the second and third and then almost holed his approach to the 603-yard eighth hole for an albatross, but missed the eagle putt from five feet and had to settle for a birdie.

With McDowell following birdies at the fourth and seventh with a bogey on the eighth, it looked like the pressure might finally be beginning to tell on the Portrush man, who had led since an opening 67 and fired another 67 on Friday.

However, it was Watson who made a vital mistake on the 10th when his simple approach to the green plugged in a bunker, from where he could only blast out to 40 feet and three-putt for a double bogey.

And to make matters worse for the left-hander, playing partner McDowell holed from 30 feet for birdie on the same hole to move to 12 under par, four shots clear of Poulter and five ahead of Watson, 2011 winner Martin Kaymer and Japan's Hiroshi Iwata.

Poulter, who had saved par after driving deep into the trees on the 11th, looked set to close the gap on McDowell when he played a superb long-range bunker shot to the par-five 14th.

However, the world number 44 charged his birdie putt from six feet some three feet past the hole and missed the return to drop a shot and fall back to seven under.

McDowell's lead was still four shots with Kaymer having birdied the 16th and Denmark's Thorbjorn Olesen also moving to eight under with four birdies in five holes from the 11th.

Watson had bogeyed the 12th after a misjudged tee shot but bounced back with a birdie on the 14th to join Poulter on seven under.

"Yes, I had a three-shot lead overnight and it's only one now, but I'll take this position any week that you offer it to me, a one-shot lead going into the last round on a golf course that I enjoy." - Graeme McDowell

Kaymer birdied the 18th to complete a superb 66 and set the clubhouse target on nine under par, which was soon within two of the lead after McDowell failed to get up and down from the left of the 17th green.

Watson had reached nine under par with birdies on the 15th and 16th only to three-putt the 17th, a hole all three of the final group bogeyed as Poulter found similar trouble to McDowell.

Iwata, who is playing in his first WGC event, birdied the 16th and 18th to complete a round of 68 and move into second place on 10 under, just one behind McDowell who failed to birdie the last for the third day running.

Watson had no such problems despite laying up into the rough, the world number seven hitting a superb approach to two feet to finish with a birdie and move alongside Kaymer on nine under.

McDowell, who has yet to win a WGC title, said after the penultimate round: "I played reasonably solid today."  

"I thought conditions were a little bit more difficult, colder, obviously a little bit of overnight rain made the golf course play a little bit longer.

"I didn't quite score as well as I did the last couple days but really gave myself some confidence from a ball-striking point of view that I can get the job done tomorrow.

"And let's be honest. Yes, I had a three-shot lead overnight and it's only one now, but I'll take this position any week that you offer it to me, a one-shot lead going into the last round on a golf course that I enjoy.

"I am excited about the challenge tomorrow and really looking forward to it.

"It would be huge to win but I can accept whatever happens. I feel like I am turning the corner from a lot of points of view, mentally, physically and in my personal life a lot of good things are going on.

"I am excited about another opportunity to win a golf tournament. If it happens I will be very happy, if not things are moving in the right direction."

McDowell admitted he had never heard of nearest challenger Iwata before this week, but the world number 127 is quite well known in his native Japan.

"I'm kind of relatively short tempered, so I always focus not to get too angry at myself," Iwata said.

"I believe I'm doing pretty good at that at the moment, so I just want to keep that going."

US Open champion Kaymer could be McDowell's biggest threat given his record at the venue, the German shot a closing 63 on his way to victory three years ago and also holds the course record of 62.

"Finally I could make some putts today, that was nice," the 29-year-old said.

 "The first two days I played really well but the putter was a little cold.

"Today I make a couple mid-distance putts, only one bogey so I think I put myself in a good position.

"Obviously you need a little help from Graeme in order to win, but I'm playing really well and that's all I can do."