MEMPHIS, Tenn. Sloppy mud one day, broiling heat the next. Lucas Glover is playing his best golf no matter the conditions on the ground or in the air, posting a 6-under 64 on Friday for a one-shot lead over Jordan Spieth in the FedEx St. Jude Championship.

Glover holed three putts longer than 25 feet, one of them for eagle on the par-5 16th, and has made only one bogey through 36 holes going into the weekend of the PGA Tours postseason opener at TPC Southwind.

It was the 19th time in his last 20 rounds Glover has shot in the 60s. A week ago, he was No. 112 in the FedEx Cup and looking at a month off. Now hes moving closer to making it all the way to the Tour Championship.

Im old enough to know it can change the other way in a hurry, too, the 43-year-old Glover said. So kind of ride the wave and just dont overthink it. Keep going and play until it runs out, and then figure it out after that.

Glover was at 10-under 130.

Spieth was up to his tricks, holing a bunker shot for birdie on the seventh hole after back-to-back bogeys, part of a late surge that gave him a 68.

For all of them, the biggest issue was the hot sun and Southern humidity, a combination that had the heat index just short of 120 degrees Fahrenheit (48 Celsius).

Eric Larson, the caddie for Harris English, had to stop after 10 holes. He stooped to tie his shoes on the second hole and had trouble standing up. English all but ordered him to get checked out. Larson said his heart rate was high and blood pressure was low (90 over 50).

He had intravenous fluids and felt better by the end of the day. English grabbed Andrew Argotsinger, the head pro at nearby Windyke Country Club, to fill in. Larson slipped him $100 for the effort when the round was over.

For everyone else, it was a matter of soaked shirts, soaked pants and plenty of birdies from the fairway on a course that had been soaked by storms the last few days.

Towels were used as much to wipe arms, necks and brows as cleaning clubs.

I didnt get this wet in the shower this morning, Glover said.

Spieth figured the heat would not be an issue coming from Dallas the last few weeks, though he conceded he played most of his golf before noon. He practically bragged to his caddie that Memphis heat was nothing to worry about.

And then today Im like, Man, I was wrong. Im humbled, Spieth said. Its just a different kind of heat. But it felt like it was just coming off the ground. Ill bring two shirts from now on and change at the turn because I was struggling a bit early in the round.

The golf part was fine, though Spieth said the heat contributed to a few poor club choices that led to bogey. Hes right where he wants to be going into the weekend, with plenty of company.

Tommy Fleetwood (66) and Sungjae Im (65) were among five players at 8-under 132. Scottie Scheffler and Rory McIlroy each had a 66 and were in the group three shots behind.

The top 50 from the 70-man field advance to the second week of the playoffs at the BMW Championship, with Cam Davis making the biggest move. He had three birdies late for a 67 that currently would have him inside the top 50.

Glover started at No. 49 and could climb as high as No. 3 with a win. Thats a long way off, especially considering 16 players are within four shots of the lead.

But its an astonishing turnaround, particularly with a long putter that he copied from Adam Scott. Glover is starting to believe it saved his career. Only once dating to the Rocket Mortgage Classic has he failed to break par he had an even-par 71 in the 3M Open in Minnesota when he missed the cut.

He finished no worse than sixth in the three tournaments before Minnesota, and he won the Wyndham Championship last week.

Ive had times where I didnt want to play, for sure, he said. But Ive also had times where I was playing terrible and something clicked on the last three or four holes and I went out and played well the next week. And that taught me a lesson pretty quick. Every shot, every opportunity, if its going wrong, you can turn it around pretty quick.

He holed a 30-foot birdie on the par-4 13th, then ran in an eagle putt from nearly 35 feet on the 16th hole. He had three birdies in a four-hole stretch on the front nine.

Spieth offset four bogeys with his share of birdies, none more special than holing a bunker shot. It was his second straight day of holing out from off the green. He chipped in for eagle on the 16th on Thursday.

As long as I carried the rough and landed it on the fringe or just on the green, I thought it would be somewhere in the 5- to 6-foot range, Spieth said. And then when it was tracking, it was right on line. I did what I could do and relied a bit on luck there for it to actually drop.