Jason Day will rely on his winning experience at the Players Championship to have any hope of reeling in leader Webb Simpson in the closing rounds at TPC Sawgrass.
World No.7 Day was left in Simpson's wake after the second round as the American fired a course record-equalling nine-under-par 63.
Former US Open winner Simpson joined six others, including Australians Day (2016) and Norman (1994), to post a 63 during golf's unofficial fifth major.
At 15 under, Simpson's five-shot cushion is the largest 36-hole lead in the tournament's history.
South Africa's Charl Schwartzel (66), American youngster Patrick Cantlay (68) and New Zealand's Danny Lee (66) share second at 10 under.
Day carded a bogey-free 67 to climb to eight under to be the leading Australian, seven shots off the pace.
He says he will draw on the positive memories of his dominant Players victory in 2016 as he attempts to chase down the equal-largest 36-hole deficit at Sawgrass, set by Tim Clark in 2010.
"It's always good to come back and know you've won on a golf course like this because it is tough, and the weekend changes," Day said.
The 30-year-old Day is also inspired to continue his hot streak after winning last week's US PGA Tour event in North Carolina.
"It gives you a lot of confidence knowing you can close even when you don't have your best stuff," Day said.
Day's countryman Adam Scott's 68 left him at seven under, while Marc Leishman (71) was five shots further back.
"It was really solid stuff today from tee to green; definitely my best (ball-striking) in a long time," Scott said.
"I'd like to have two more rounds in the 60s and see where that leaves me after 72 holes because I think the course is going to firm up; I don't think (officials) want 25 under winning the tournament."
Rounding out the Australian contingent was Cameron Smith (75, seven over), Geoff Ogilvy (74, eight over) and Rod Pampling (80, 10 over) who all missed the cut.