But former World No.1 Day has hit the rest button and hopes his realisation leads to a fruitful run through the PGA Tour's Playoffs series – starting with this week's Northern Trust event in New Jersey.

Day hired New Zealand's Williams – who caddied for Woods during 13 of his 15 major wins as well as Adam Scott's 2013 Masters victory – at June's US Open at Pebble Beach but has had little success since.

In the five events Williams has caddied for Day, the Queenslander has recorded just one top-10 result while he missed the cut at the Open Championship.

Having once held the No.1 position for 47 straight weeks, World No.21 Day is no longer Australia's top-ranked golfer with Adam Scott one spot higher.

Day concedes he set the bar too high for himself after what was a serious change for an elite professional golfer.

"I may have put a bit too much pressure on myself with regards to trying to play too well," an honest Day told AAP at host venue Liberty National in New Jersey on Wednesday.

RIGHT: Day and Williams have worked together since the US Open at Pebble Beach. PHOTO: Andrew Redington/Getty Images.

"Having a new caddie on the bag is a change and I'm trying to work everything out.

"I just haven't pieced everything together at an event and I need to get on top of that."

But the 31-year-old said there were plenty of positives of his partnership with Williams, most importantly that his work ethic has increased dramatically.

"You want it to be successful and it is in the sense I wanted to work harder and Steve is certainly making me do that," Day said.

But Day is hoping the intensity of the PGA Tour's FedExCup Playoffs, in which 125 contestants are vying for their share of US$78.5 million (AU$116m) prize pool, can reignite a spark.

Day was once a perennial contender at the Playoffs, particularly the Northern Trust, winning in 2015 in addition to four top-six results at the finals opener.

"This is crunch time and we will see how it goes," Day said.

The Northern Trust features the top-125 golfers on the FedExCup standings from the regular season.

Day is joined in the field by fellow Australians Scott, Marc Leishman, Cameron Smith, Aaron Baddeley and Matt Jones.

- Evin Priest, Australian Associated Press