Australian teenage prodigy Ryan Ruffels took advantage of a sponsor's invite to the Arnold Palmer Invitational to shoot a first-round 69 and be two shots off the lead, while Jason Day also made a bright start in Orlando.

Ruffels took full advantage of his sponsor's invite to the prestigious Bay Hill tournament, firing a 3-under-par score to sit in a share of sixth, alongside compatriot Greg Chalmers, after the first round.

The 18-year-old Victorian will start the second round just two shots back of leaders Matthew Fitzpatrick of England and Argentine Emiliano Grillo.

World number two and defending champion Day, and Aaron Baddeley are among a group of 12 tied for eighth place after posting rounds of 2-under 70.

"All my friends are either at university or on gap years and I have few golf mates playing on mini tours, so I guess you could say they probably wish they were doing what I am," Ruffels said.

"To have these opportunities as an 18-year-old is about as good as it gets."

Ruffels, the son of former Australian tennis professional Ray and US Federation Cup player Anna-Maria Fernandez, turned professional in January 2016, aged 17.

Considerable hype followed him, courtesy of strong finishes at the 2014 and 2015 Australian Open, in addition to winning a world junior championship.

Yet Ruffels has been forced to battle recently on the US PGA Tour's third-tier South American circuit after missing the 2016 FedEx Cup's top 200 by a single point, despite making four cuts in seven sponsor's exemptions.

"It's a great feeling, this is where you want to be eventually," Ruffels said.

"It's nice to be back on the US PGA Tour and even better to be playing well today."

Ruffels said he would lean on mentors Day and 2006 US Open champion Geoff Ogilvy, as he looked to book a full card on the lucrative US PGA Tour.

"It's humbling to have major winners like Geoff and Jason to believe in you and be in your corner," he said.

AAP