Cameras caught the US superstar gobbing onto the grass during the morning session of the opening day.
Three-time Major champion Koepka was left shaken earlier in his round when he left a female fan bloodied after smacking her in the eye with a wayward drive.
Koepka, 28, went to check she was OK as soon as he approached the horrific scene by the sixth green.
But it was his actions later on that left fans disgusted.
After footage showed him spitting in full sight of fans and cameras, one wrote: "Koepka spitting on tees and greens like a filthy pig."
Another user said: "Koepka spitting a gobfull on the tee. Disgusting."
Former Olympic gold medallist hockey star Sam Quek put a sick face emoji after posting: "… That's the third time I've seen a close up of Koepka spitting."
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One comment read: "#Koepka Shame on you – spitting on the golf course – what are you teaching our younger players?"
Another said: "Does Brooks Koepka spit on himself on every hole?"
Koepka has previous for spit storms.
At last year's Open he denied spitting on the ninth green at Royal Birkdale.
And n November 2016, television cameras appeared to show him spitting on a green at the Turkish Airlines Open, an event he won in 2014.
Koepka and playing partner Tony Finau beat Justin Rose and Jon Rahm one up in the first fourballs match today.
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