Koepka thinks DeChambeau plays slow -- and has said so on a few occasions, including at last year's Northern Trust tournament where DeChambeau endured considerable criticism.
DeChambeau, after an intense fall workout program that has seen him put on 25 pounds, took his own shot at the No. 1-ranked player, and it had to do with his fitness.
"Yeah, I weigh more than him right now. Considerably more," DeChambeau was quoted as saying by Golf Digest on a Twitch feed. "Did you see the [ESPN] body issue? He didn't have any abs. I have abs."
Koepka responded via Twitter, saying he is "2 short of a 6 pack," with a photo of his four major championship trophies -- two each for the U.S. Open and PGA Championship.
Playing his first tournament since a setback with a knee injury in October, Koepka opened the Abu Dhabi HSBC Championship with 6-under-par 66 on Thursday to finish two back of the leaders. DeChambeau shot 72 in the European Tour event.