McIlroy has gone left hand low after he blamed poor putting for missing the cut in last week's event when he was four over par after 36 holes because of some erratic tee to green work but mostly uncertain putting..
"I feel like my left hand controls my putting stroke and that's the lead hand for me," McIlroy said. "But over the last few weeks I have felt like my right hand was becoming a little bit too dominant and a little too active in the stroke.
"So I practised with the new grip over the weekend and it felt really, really good. The roll of the ball was really good. The contact is much better and it just takes my right hand out of it. I really feel like I'm controlling the stroke with my left hand only. So I'm going to give it a try this week and see where we go with it."
It was not a stop-gap fix, McIlroy promised.
He was concerned last week when his right hand became too dominant and he missed putts on the left hand side of the hole. He had practised a lot with his new grip and it felt natural.
"So I thought, 'why not give it a go?' "
In 10 PGA rounds this year, McIlroy averages 29.71 putts a round compared to Spieth's 27.29.