Cameron Smith will need to conjure one of his signature Sunday charges and match the record of the legendary Arnold Palmer to claim an unlikely US Open victory.

Australia's reigning British Open champion was one of many players to struggle on the brutal Los Angeles Country Club layout on Saturday (Sunday AEST).

Despite climbing from outright 10th to a tie for ninth, Smith's one-over-par 71 left him seven shots behind US co-leaders Rickie Fowler and Wyndham Clark entering the final round.

Smith at least finished his day on a high, draining a 20-foot birdie putt on the final hole after bogeys at 16 and 17.

But he was put in the shade by playing partner and world No.1 Scottie Scheffler, who holed out for eagle at 17 and then followed Smith in with a long birdie putt on the 18th to move up to outright fourth at seven under.

Smith can at least draw on his own recent history as he looks to make a charge in the final round.

He closed with an eight-under 64 in the British Open at St Andrews last year, coming from four shots back to run down Rory McIlroy and claim a maiden major triumph.

The 29-year-old also had an equal-low final-round 65 to post his best PGA Championship finish last month.

Seven-time major winner Palmer holds the record for the greatest final-day comeback in US Open history, when he stormed home from seven shots back to win at Cherry Hills in 1960.

Smith acknowledged he would need "probably one of the best rounds of my life" to claim the US Open trophy.

"It's going to have to take at least five or six, probably even seven-under, I think," he said.

"The golf course is getting tougher, but there's still lots of wedges out there.

"The leaders are there for a reason, as well. They're obviously playing really good golf."

Fowler blew the chance to hold the outright third-round lead in LA after he three-putted the final hole for a bogey to slip back to 10 under with Clark.

Northern Irishman McIlroy (69) was outright third at nine-under 201 as he chases a fifth major crown and his first since 2014.

Min Woo Lee did it still tougher than countryman Smith on Saturday in California.

After carding the low round of the day on day two - a brilliant five-under 65 - to be in a tie for sixth, Lee struggled to a four-over 74 to slip back to 12th at two-under 208.

His American playing partner Sam Bennett had an even dirtier day, eventually signing for a nine-over 79 to tumble all the way to a tie for 47th.

Lee is bidding to join his two-time major winning sister Minjee Lee as a US Open champion.

The other five Australians missed the halfway cut in at the prestigious Los Angeles Country Club, which is hosting the US Open for the first time.