Kramer Hickok and Satoshi Kodaira share the one-stroke lead after the opening round of the Travelers Championship, where stars Bryson DeChambeau, Brooks Koepka, Phil Mickelson and Dustin Johnson were forced to take a backseat.

Unheralded duo Hickok and Kodaira upstaged the star-studded field following their seven-under-par 63s at TPC River Highlands on Thursday.

Hickok – searching for his maiden PGA Tour title – offset a bogey at this first hole with eight birdies as the American golfer posted a career-low round in Cromwell, Connecticut.

"I really only hit one bad putt — on the par-five 13th. Other than that, I just felt like the holes looked awfully big today," the 29-year-old said. "I made a lot of good putts today, and the greens says are rolling so good that just the holes look big."

Japan's Kodaira matched his best score on the PGA Tour, from the second round of the 2018 RBC Heritage – his only victory.

Kodaira holed out from the fairway for an eagle on the 348-yard par-four second hole.

"I knew it was on target but didn't see it go in," he said. "I heard the applause, so I knew it went in."

Talor Gooch is a shot behind Hickok and Kodaira, while Maverick McNealy, Brice Garnett, Beau Hossler, Henrik Norlander and Patrick Rodgers are a stroke further back heading into the second round.

There is a 31-player logjam tied for 45th position at one under, headlined by DeChambeau, Koepka and Mickelson.

DeChambeau, who was dethroned by Jon Rahm at last week's U.S. Open, mixed three birdies with two bogeys to start his Travelers Championship campaign.

Four-time major champion Koepka also shared an identical round, while US PGA Championship winner Mickelson had four birdies and two bogeys.

"I'm awful the week after a major, especially U.S. Open, because it takes so much out of you," said Koepka, who was tied for fourth behind Rahm at Torrey Pines. "But still should have played better. No excuse. I mean, I'm kind of tired. I am going to enjoy getting to bed tonight."

The likes of Patrick Reed, Adam Scott, Jason Day and Rickie Fowler also shot 69s in round one.

Defending champion Dustin Johnson – who slipped to second in the golf rankings following Rahm's U.S. Open triumph – started his bid for back-to-back titles with an even-par 70.