SHANGHAI — Dustin Johnson started with a five-shot lead and made 10 birdies. Two swings kept him from running away from the field Saturday in the HSBC Champions.

The only consolation was a 6-under 66, which gave Johnson a three-shot lead over defending champion Ian Poulter going into the final round of this World Golf Championship. It was the final hole — a three-shot swing — that irritated the 29-year-old American.

On a Sheshan International course set up for low scoring, Poulter made birdie on the par-5 18th for a 63. Three groups later, Johnson hit a bad drive at the worst time and watched it sail to the right and into the lake. Wanting to be sure he didn’t drop it in the wrong spot, Johnson returned to the tee and wound up with a double bogey.

It was his second double bogey of an otherwise remarkable round.

After making five straight birdies to start to pull away, Johnson saw his wedge roll back down the hill three times before the fourth one hit the pin at No. 10. He still had to make about a 12-foot putt to escape with double bogey.

Johnson was at 18-under 198 and will be in the final group with Poulter and Graeme McDowell, who had a 64 and was four shots behind.

“I have to do my thing tomorrow,” Poulter said. “It’s only Saturday. You can’t win tournaments on Saturday. It’s all about playing well on Sunday. I need to do that. I need to make plenty of birdies, try to make an eagle. If I can, I can get close.”