MEMPHIS, Tennessee: Hideki Matsuyama felt his lower back starting to act up. On a whim, he decided to put a new putter in his bag for the start of the PGA Tour postseason. And now the Japanese star has a five-shot lead going into the final round of the FedEx St. Jude Championship.

“I am surprised,” Matsuyama said through his interpreter, breaking into a big smile when he added, “but I did play well today.”

He played well enough for a second straight 6-under 64 that enabled him to pull away from a crowded field and put plenty of distance between him and Nick Dunlap.

Matsuyama quickly atoned for an early bogey by drilling a 3-wood over the water to 15 feet and making the eagle putt. He kept adding birdies the rest of the day in more steamy weather and no one could stay with him.

Denny McCarthy, who was tied for the 36-hole lead with Matsuyama, put four bogeys on his card before registering his first birdie. Sam Burns had only five pars — and a broken driver — in his round of 70 to fall back. Scottie Scheffler lost ground with a few suspect chips and was seven shots behind after a 69.

“I felt like I got away with some stuff, so hopefully clean it up a little bit and give myself a lot more opportunities,” Scheffler said.

Scheffler was at 10-under 200 along with Burns, who slammed his driver to the ground on No. 9 and the head broke off. He made double bogey to go with five bogeys and seven birdies. It was quite a day.

Dunlap did his best to stay close and was within three shots until one wild drive too many. He went so far right on the 12th that he cleared the water and landed on the other side, and then managed to save par. But he hit right again on the 13th in deep grass, couldn’t reach the green and took bogey.

He shot 66 and will be in the final group, extending his remarkable run. A year ago, he was winning the US Amateur at Cherry Hills. He won The American Express in January as an amateur, turned pro, and then won the Barracuda Championship last month.

“I should be playing the US Am this week, and I just got done playing a round of golf with Scottie. It was pretty cool,” Dunlap said.

Dunlap is among five players with multiple wins this year and still was a long shot to extend his season. He was No. 67 in the FedEx Cup because he was an amateur for his first PGA Tour title and received no points.

Even if he can’t catch Matsuyama, Dunlap has a chance to not only be among the top 50 who advance to the BMW Championship next week, but lock up a spot in the Tour Championship for the top 30.

Matsuyama was at 17-under 193 and in position to capture his first FedEx Cup playoff event.

But this postseason opener was all about moving on. The top 50, along with getting to the next playoff event outside Denver, are assured of getting into all eight of the $20 million signature events next year.

Viktor Hovland, the defending FedEx Cup champion who started this postseason at No. 57, took a big step toward advancing with a 66. He was alone in third, six shots behind.

“The ball is starting to behave like I’m expecting it to,” Hovland said. “The misses are way smaller than they used to be. Before they would be off the planet, whereas now it’s manageable and I can make a nice up-and-down or make a long putt or whatever it is.”

Jordan Spieth’s season effectively ended when he made two double bogeys in his round of 74, leaving him in 69th place against a 70-man field.

Will Zalatoris came into the postseason at No. 49 and shot 67 on Saturday. He was tied for sixth and all but assured of staying well inside the top 50.

Among those on the bubble to advance going into Sunday are Justin Rose and Adam Scott. Rose is No. 55 in the FedEx Cup and was tied for ninth after 54 holes at the TPC Southwind. He shot 71 on Saturday after making double bogey on the last hole. Scott is at No. 46. He shot 68 and was projected inside the top 50 going into the last day.

Others projected to be just inside the top 50 include Harris English, still coping with a bad back, and Phoenix Open winner Nick Taylor.

Rory McIlroy, who was seen playing tennis after his opening round in sweltering heat on Thursday, had a bogey and two double bogeys after just four holes Saturday. He shot 74 and was toward the bottom of the pack. But he could afford a lackluster week having started at No. 3. He was projected to fall no more than a spot or two.

Matsuyama has three top 10s in his last six starts, including the bronze medal he won at the Paris Olympics. Why change putters? He’s not really sure.

“I’ve had the putter for a while, and I thought it might be a good week to debut that putter,” Matsuyama said.

He leads the field in the key putting statistic, gaining on average nearly seven shots against the field. He also has 19 birdies and an eagle.