WGC Champions: World number one Dustin Johnson leads in Shanghai

Johnson had a new putter made for day two of the WGC Champions

World number one Dustin Johnson hit four birdies in his final four holes to take a one-shot lead at the halfway stage of the WGC Champions in Shanghai on Friday.

The 33-year-old American's incredible nine-under-par 63 saw him overtake compatriot and overnight leader Brooks Koepka, who hung on for second on 12 under.

England's Justin Rose, 37, and Thailand's Kiradech Aphibarnrat are four shots back in a tie for third on nine under at 'Asia's major'.

American Patrick Reed, 27, is five shots off the lead in fifth after his two-under-par 70.

Sheffield's Englishman Matthew Fitzpatrick, 23, was sixth after an impressive 69, including six birdies overall.

Johnson, who triumphed in Shanghai in 2013 and has won all four prestigious World Golf Championships (WGC), followed up his opening 68 with a sparkling round that started well and got better.

Early in his second round, the South Carolinian had a couple of near birdie misses, but found his range with back-to-back birdies on holes 12 and 13, then ramped up his challenge to finish with a flourish.

Johnson, tied 11th after the opening round, said he had switched putters less than 20 minutes before his second round with remarkable effect.

"I wasn't really pleased with the one I played with yesterday so the guys here in China made me one," said the 2016 US Open champion.

"I got it right before I walked to the tee. I hit a few putts on the practice green with it and I was like, 'Oh, this will work pretty well'.

"I went out and holed a lot of putts today, so I kind of like it."

Justin Rose bogeyed at the 18th hole

Koepka, whose first major title came at the US Open in June, stayed in contention with a solid 68 at a sunny Sheshan International Golf Club.

The 27-year-old began his second round with real intent, reeling off two birdies to start the second day much as he finished the first.

Rose's second round would have been even better but for a bogey at the 18th and he carded a 68 to go with his first-round 67.

"Listen, it's part of the 18 holes," Rose said of his stumble. "It's a disappointing way to finish, I felt like I was running out of steam a little bit coming in."

But defending champion Hideki Matsuyama, the world number four from Japan, again failed to fire.

He followed up his disappointing opening-round 74 with another two-over 74 as his challenge disintegrated.