Thursday, 14 September 2017: Jason Day says reigniting his sensational 2015 form with the driver is key to a return to the top of the golf world.

A return to the site of his landmark 2015 BMW Championship win has reminded Jason Day of the importance of rediscovering his world-beating form with the driver.

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While walking the fairways of Conway Farms Golf Club during a practice round on Wednesday, Day acknowledged his current form off the tee lacks the potency he enjoyed during a six-shot victory in Chicago two years ago.

"Walking around this course, you realise how good I drove it that week. I was hitting the ball so well and I was in portions of the fairways where I was playing a different game of golf," Day told AAP.

Day blitzed the field at Conway Farms for his fifth US PGA Tour victory of 2015, securing a debut stint as the world No.1 golfer.

He ranked third on the US PGA Tour with an average drive of 313.7 yards, but has slipped to 21st during a winless 2017 season.

Now ranked 28th in the FedEx Cup standings, the 29-year-old's season will be over unless he finishes with at least a 30th place at the BMW to progress to next week's Tour Championship - the finale of the Tour's play-offs series where the leading points scorer bags a $US10 million ($A13 million) bonus.

With two top-10 results in his past three starts, including the PGA Championship in August, Day is confident of earning his seventh trip to the Tour Championship in Atlanta.

"Things are looking up. Being No.28 in the FedEx, I really want to get to Tour Champs, so that's the ultimate goal for me right now," Day said.

The Ohio-based Queenslander's preparation for the BMW has been hampered by a week of back spasms and an indefinite split from long-time caddie Colin Swatton.

"I couldn't do much practice and I'm coming into this event a little underprepared," admitted Day.

"The chemistry between Col and I (diminished) slowly over time. Obviously this is a very hard time for both of us; we had a (player-caddie) relationship for (17 years)."

But Day is confident of channelling the good vibes from 2015 and bagging his first win on Tour since May 2016.

"To be able to come back to a course like this is great for the confidence; being back here reminds you of the level of golf you know you can play."