The 26-year-old shot a disappointing six-over par on a course that proved a demanding examination of the players' driving, approach play and putting.
Unfortunately for Bob, bogeys instead of birdies on the three par fives - which included a double on the fourth hole - summed up a round where the Glencruitten man just never got going.
He was not alone in finding it tough at the Rochester venue as world No 17 Tyrrell Hatton, Jon Rahm, US Open champion Matt Fitzpatrick and Jason Day, last week’s winner on the PGA Tour, all posted the same score as MacIntyre.
Bob, who has made the cut in all 10 of his previous major appearances, sits in a tie for 117th, with 30 players still to finish following a frost delay of just under two hours at the start of the day. He will know it is going to take a big performance to not only move back into any sort of contention, but just to make the weekend.
The Oban man had declared himself back to full fitness after a back strain hampered his preparations, but had opened with three straight pars before running up a six at the yawning 617-yard 13th.
Back-to-back dropped shots at the eighth and ninth and another bogey at the third was followed by the afore-mentioned double-bogey at the fourth. His only birdie came at the 8th hole when a brilliant iron shot saw him tap home from just under four feet.
As he dissects what he needs to do ahead of his scheduled 12.33pm tee off today, Bob will take consolation from the fact he ranked in the top 50 in terms of fairways hit, but will know improvement is needed on his placings of 123rd around the green and 152nd with the putter.
More tough conditions are predicted today, and it is likely Bob will need to shoot somewhere around level par or better to protect his unblemished cut record in the majors. He is certainly capable.
Coverage of the tournament continues today on Sky Sports.
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Of those finished, the LIV Golf player holds a one-shot lead over world No 2 Scottie Scheffler and Canadian Corey Conners. “It’s a fantastic round at Oak Hill,” said DeChambeau. “It’s a prestigious place. Very difficult golf course. As I was looking throughout the week, I’m like, ‘Man, I don’t know how shooting under par is even possible out here on some of the golf holes.”
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