The 41-year-old Australian, who plays on the LIV Golf circuit with his great pal Cameron Smith, reckoned he was used to much speedier rounds on the Saudi Arabian-funded tour than Thursday's seemingly eternal slog in ever changing weather conditions.
The three-ball groups were actually taking about six hours to get round but Leishman was among those getting frustrated at frequent, long waits at the tee. For instance, there were hold-ups of nearly 10 minutes on the par-five seventh.
Leishman was unlucky to get caught up with some of the worst weather around lunchtime as the rain careered down.
"It felt like we were on the golf course for about 12 hours. We'd been on the course for three hours through eight holes," he said after his two-over-par round of 73.
"That was tough to deal with, especially coming from somewhere (LIV Golf) where we play a round in under four-and-a-half hours.
"You have to deal with all that sort of stuff and I felt like I dealt with it decently well. Just got a little frustrated there."
Asked if he'd been told what was causing the delays, he just shrugged: "No, just everyone takes their time."
The Victorian didn't blame the build-up of the dawdling pace, as he went round with former champ Stewart Cink and Italian Matteo Manassero, as a factor in his final-hole bogey, but Leishman was "pissed off" his round should end so anti-climactically.
The high-powered group of newly crowned US Open champion JJ Spaun, Spanish superstar Jon Rahm and defending champion Xander Schauffele, was put on the clock.
They took five-and-a-half hours to reach the 18th fairway, with Spaun warned after exceeding his allotted 50-second time limit on his approach to the previous hole.
United States Ryder Cup captain Keegan Bradley reckoned the snail's pace was to be expected.
"Major championships are long and when you get out here on these blind tee shots with the wind, and you're going to have guys hitting it in the junk, then it's going to take a while to find it," he said.
With agencies
