The LIV Golf rebel, who famously bulked up for his brand of big-hitting golf, has performed a U-turn in recent weeks with a completely transformed diet.
And the decision appeared to pay dividends following a four-under-par opening round at Oak Hill Country Club.
Afterwards, he said: “It’s a fantastic round of golf at Oak Hill. I was looking at it throughout the week and was like, ‘man, I don’t know how shooting under par is even possible here on some of the golf holes’.
“Luckily, I was able to play some really good golf, hit a lot of fairways, did my job and made some putts.”
The start to the opening round had been delayed by frost and darkness curtailed the day’s action with a number of players - 11 groups in all - still to complete their first 18 holes.
Among them was another LIV convert in Dustin Johnson, who was a shot behind DeChambeau on three-under with one hole still to play alongside countryman Scottie Scheffler.
Relatively unknown American Eric Cole has the on-course lead at five-under after the opening 14 holes.
It proved a mix day for Europe’s stars. Rory McIlroy, who admitted he was dealing with some unspecified illness in the lead-up, battled his way around the course to stay in contention at one-under.
But Masters winner Jon Rahm, of Spain, had a horror round as he ended up six-over par alongside England’s Matt Fitzpatrick.
"I'm fighting something," McIlroy said.
"I thought I got a great night's sleep last night and I looked at my Whoop (personal fitness monitor) and I was 22 per cent recovery, and my skin temperature was 3.5 degrees higher than what it's been.
"But I actually feel better today than I felt yesterday, so plenty of water and a bit of rest, I'll be fine."