Dustin Johnson lines up a putt during the third round of the Northern Trust on Saturday in Norton, Massachusetts. Photo: VCG

Dustin Johnson curled in a 40-foot eagle putt on the 18th hole to seize a five-stroke lead after Saturday's third round of the US PGA Northern Trust tournament.

The 36-year-old American fired a seven-under-par 64 to follow up his stunning 60 on Friday and stand on 22-under 191 after 54 holes at TPC Boston.

"I was just worried about shooting as low as I could again," Johnson said. "It was good. I played solid all around. I gave myself a lot of opportunities. "I hit a lot of quality iron shots. I was swinging really good. I hit it in the fairway. It's nice when everything matches up."

Johnson grabbed the largest 54-hole lead on the PGA Tour this season with Scottie Scheffler, coming off a 59 on Friday, and Harris English sharing second on 196. South African Louis Oosthuizen was fourth on 198.

Fourth-ranked Johnson would return to the world No.1 spot with a win if Spain's top-ranked Jon Rahm and US world No.2 Justin Thomas finish worse than a three-way share of second. Rahm shared 19th on 203 while Thomas was level 34th on 206.

Johnson, who matched a PGA record with a 27 on the front nine Friday, settled for only four birdies Saturday - a tap-in putt at the par-five second, a six-footer at the fifth, an eight-footer at the par-five seventh and a 20-footer at the par-three eighth.

Despite a 50-minute weather delay just before Johnson made the turn, he stayed strong, putting his approach inches from the cup at the par-four 12th and tapping in to reach 20-under.

Johnson made bogey at 13, finding a greenside bunker and missing an 11-foot par putt, but answered with an 18-foot birdie putt at 17.

On the par-five 18th, Johnson reached the green in two with a 40-foot eagle putt, angled the ball over a ridge and left of the cup then watched it roll back into the hole.

English briefly shared of the lead with a run of three birdies in four holes, capping the streak at the 14th by rolling in a chip shot from 42 feet. But English stumbled with bogeys at the par-three 16th and par-four 17th, missing par putts from just inside five and seven feet.

The event is the first US PGA playoff tournament, with the top 70 players in season points advancing to this week's BMW Championship, from where the top 30 will advance to the season-ending Tour Championship next month at East Lake in Atlanta.

Tiger Woods shot 73 to stand on 67th at 212, one stroke ahead of playing partner Rory McIlroy, who fired 74.