In an ominous sign for the US Open field, defending champion Dustin Johnson believes he's back to the sensational form that catapulted him to golf's world No.1 ranking.
The big-hitting American ended Australian Jason Day's 47-week tenure at the top during a hot run earlier this year with back-to-back World Golf Championship titles among three victories.
But Johnson's momentum was cruelled with a freak fall down a staircase on Masters eve in April and he hasn't bagged a top-10 result on the US PGA Tour since.
On the eve on the US Open, 'DJ' believes he's on the cusp of the world-beating form that saw him bag six international wins between his maiden major title at the 2016 US Open and the WGC-Match Play in March.
The 32-year-old Johnson warned the 156-player US Open field his best golf would be unbeatable this week at Wisconsin's debut host Erin Hills.
"Absolutely (it's unbeatable); no doubt," said Johnson, whose wife Paulina Gretzky gave birth to the couple's second son, River Jones Johnson, on Monday.
"Leading into the Masters, I was playing the best golf I've ever played.
"It's taken me a while to get back to where I was."
However, former US Open winners Jordan Spieth and Rory McIlroy won't be counted out.
Four time-major winner McIlroy believes the wide fairways at the 7,100-metre Erin Hills suits his devastating skill with the driver.
World No.2 McIlroy ranks second on the PGA Tour for strokes gained off the tee and fifth for driving distance with his average of 308.5 yards.
"That's why I like this golf course, it allows you to be aggressive and swing freely and get after it," the 28-year-old said.
World No.5 Spieth compared the uncertainty of Erin Hills to his 2015 US Open victory at Chambers Bay, which was also a rookie host.
"A brand-new golf course limits any kind of experience players have," the two- time major winner said.
"So any experienced major contenders may have; everyone has the same amount of work to do."
Jason Day leads a five-strong Australian contingent this week and the 29-year- old Queenslander is coming off a second-place finish at the Byron Nelson Classic in May and a 15th at the Memorial Tournament in Ohio.
The world No.3 is looking to go one better than his two runner-up finishes during a stellar six US Open starts that have yielded five top-10s.
Day is joined by world No.12 Adam Scott, No.35 Marc Leishman, Nick Flanagan and Wade Ormsby.