Americans Austin Cook and David Lipsky are among the first round co-leaders at the Bank of Utah Championship, with only another three tournaments remaining.

In a nine-way tie for 12th at the event is Harrison Endycott. The Australian is No.238 in the standings and needs a big finish to the season. His four-under 67 included seven birdies and three bogeys.

Jason Day (68) and Karl Vilips (No.92) are a shot further behind, with the latter on the cusp and needing to play well.

Vilips had five birdies and two bogeys, while Day enjoyed six birdies with three bogeys, including his final hole.

Cook, who started at No.204 in the standings but jumped to No.96 after his round, avoided a qualifier and took advantage with six birdies, before darkness halted a slow round at Black Desert.

He was at six-under and facing a 20-foot birdie putt on the reachable par-4 14th when it was too dark to continue. The afternoon tee times had been pushed back by 15 minutes. The 38 players who did not finish were to resume at 8am.

Cook had few such complaints. A one-time winner on the PGA Tour, this is only his eighth start of the year. He was well down the alternate list and at the beach with his family, planning to play the Monday qualifier.

"Saturday got all the way down to first alternate. I felt like I was going to get in, so I helped drive everybody home on Sunday and flew out Monday and on the plane I got a text," he said. Cook replaced Erik van Rooyen, who had withdrawn.

Lipsky, starting at No.99 in the Cup standings, eagled his final hole to find himself part of a four-way tie which includes Thorbjorn Olesen (No.115) and Jesper Svensson (No.116).

The 37-year-old Lipsky has won on the European and Asian tours, but not yet on the PGA Tour.

Olesen was also surprised with his start. He was in Mississippi for the Sanderson Farms Championship, then the Dane headed back to Europe to play in the Spanish Open, went to his home in Dubai and then came to Utah. It was a lot of time in the air.

"I would say my expectations were pretty low this morning," Olesen said. "But did some recovery work the last few days and just tried to get the body ready for today."

The seven-man group one shot behind at 66 includes Paul Peterson, who was two-over for his round through eight holes until finishing with six birdies and an eagle.