Open champion Shane Lowry admitted he was still feeling the pressure of chasing a second major title despite the US PGA Championship being played without fans at Harding Park.
Playing alongside defending champion Brooks Koepka and US Open champion Gary Woodland, Lowry carded a two-under-par 68 on Thursday to lie three shots off the lead held by former world number one Jason Day and Brendon Todd.
"I said to the lads walking down the first, we wouldn't have had the ideal group or the ideal tee time, two groups ahead of Tiger (Woods) around here would have been a bit different," Lowry said.
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"The crowds would have been huge and they would have been moving an awful lot and it would have been tricky.
"The atmosphere is different, but it still gets my attention. I don’t know about the other guys, I can only speak for myself going out there, but driving to the course this morning, this week gets my attention.
"I was feeling like I was driving to a big event and on the first tee I was feeling it a little bit. I was kind of anxious to get going, like I would be at any major.
"This is a huge event. It doesn’t matter whether it’s 50,000 people here or no one. It would be nicer if there was 50,000 people here, but we all know how big this event is and how much it would mean to the winner at the end of the week.
"You’re out there trying your hardest and doing your best."
Playing alongside Tiger Woods and Justin Thomas, Rory McIlroy shot a round of 70 which saw him battle back from a hat-trick of bogeys on his front nine with three birdies in four holes around the turn.
However, the world number three was left ruing a number of missed opportunities to be closer to the pacesetters.
"It was there for the taking today," McIlroy said.
"I feel like I definitely could have been a few shots lower, but I sort of grinded it out and, with how I hit it on the back nine, even par actually wasn't too bad.
"Need to hit a few more fairways tomorrow to try to attack some pins and get it closer, and not leave myself four and five-footers for par all day."