Los Angeles - Reigning Open champion Jordan Spieth and fellow 2017 major winners Justin Thomas and Brooks Koepka are among contenders in the PGA Tournament of Champions opening on Thursday in Hawaii.

Defending event champion and 2017 PGA Championship winner Thomas, US Open champion Koepka, Spieth and long-hitting Dustin Johnson lead a set of US stars into the 34-player field at Kapalua for the first US event of 2018.

"The unknowns are very exciting right now," Spieth said.

Spieth cited a new group of rising stars, a solid group of veterans and even the latest comeback of 14-time major winner Tiger Woods in his excitement for the new year.

"With the amount of depth and talent at a younger age mixed with the guys in their 30s that are playing... some other phenomenal players that you would call maybe in prime and then the major question, which is what's it going to be like with Tiger coming back, within the next six months, it's a pretty special time to be a part of professional golf," Spieth said.

Global challengers include Japan's Hideki Matsuyama, Spain's Jon Rahm, Australians Marc Leishman and Cameron Smith, Sweden's Jonas Blixt and South Korean Kim Si Woo.

The field boasts an average age of 29.7 years, the youngest since at least 1970.

Thomas won last year's Tournament of Champions and the following week's Sony Open in Hawaii plus his first major title on the way to collecting the PGA Tour FedEx Cup playoff crown.

The Plantation Course at Kapalua played as the easiest course on the US tour last season.

"It's just a great way of, not easing into the year, but get the year going, because of how relaxing it is," Thomas said. "The course is great. There are obviously some great places to eat. And who doesn't like being in Hawaii?"

Spieth, who shook off memories of a final-round 2016 Masters meltdown to claim his third major crown last year at Royal Birkdale, says he has turned a corner mentally entering the new year.

"Starting 2018 I'm kind of ready for anything," Spieth said. "I'm ready for failure, for success, and everything in between."

Spieth has two wins and two runner-up efforts in his past eight events and three top-three finishes in his past three Maui starts. And he's engaged to long-time girlfriend Annie Verret.

"I'm just in a fantastic place compared to where I was last year," Spieth said.