(Reuters) - World number one Jason Day, U.S. Open champion Dustin Johnson and second-ranked Jordan Spieth command the spotlight at this week's WGC-Bridgestone Invitational in Akron, Ohio where Rory McIlroy is a conspicuous absentee.

Two years ago, four-times major winner McIlroy clinched the prestigious title at Firestone Country Club by two shots but he will not be competing in the 2016 edition as he is playing instead in the European Tour's French Open.

Traditionally, the Bridgestone Invitational is held in early August but the PGA Tour event was brought forward by more than a month this year to accommodate golf's return to the Olympic Games in Rio de Janeiro.

Masters champion Danny Willett of England has also opted to tee it up in Europe this week but the elite field at Firestone can still boast 16 of the world's top 20 players in the last of the season's four World Golf Championship (WGC) events.

"I'm excited to be back here ... any time you're in a World Golf Championship, it's a big event," American Spieth told reporters while preparing for Thursday's opening round.

"Smaller field this year, and some of the guys are over in France, but still, it's such a challenging golf course, one that looks like it's going to firm up, which I liked last year.

"State of the game? Pretty good," said Spieth, who tied for 37th on his U.S. Open title defense at Oakmont two weeks ago in his most recent PGA Tour start. "Trying to ramp things up for the remainder of the season. Excited about this week."

Australian Day, the game's hottest player over the past 12 months with seven tournament wins worldwide, has always relished the look of Firestone where he tied for fourth in the 2011 Bridgestone Invitational.

"I definitely like this golf course, I like the grass, I like the green speeds," said the 2015 PGA Championship winner. "With previous experience here being close to winning, knowing what I need to do to win, I feel confident about my game.

"I've had a good week off, and I've practiced pretty hard, prepped very well coming into this week. I feel very rested physically but more so mentally."

Like Spieth, Day embraces being part of an elite field gathered at Firestone this week where just 61 players will be gunning for the title.

"Obviously there's a smaller field ... I'm looking at it as a positive that that's less guys that I have to try and beat, which is fantastic," Day smiled.

"But overall, I've just got to go out there and play well. If I can do that, hopefully I'm there on Sunday."

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Frank Pingue)