Dustin Johnson has 19 PGA Tour titles to his name but insists winning is not easy as he prepares to defend his Tournament of Champions crown.

Victory at Kapalua 12 months ago represented the first of three tournament successes in 2018 for Johnson, who rated his year as "solid" on Wednesday.

The laidback Texan has managed at least one PGA Tour triumph in every year since his rookie season in 2008, but offered an amusing response when he was asked how he convinces people it is hard to win when he does it so much.

"Well if it wasn't as hard, I'd win more," said Johnson with a smile in his pre-tournament news conference, before stating he never takes success for granted.

Reflecting on the previous year, which also included successes at the St Jude Classic and Canadian Open, the world number three added: "I'm okay with it. I feel like I had a good year.

"I'd have liked to have had a little better performance in the majors, but other than that I felt like my year was good. I had a lot of chances to win and I won three times, [had] a lot of top 10s.

"It was a solid year. I just didn't contend in the majors like I wanted to.

"If I can win three times [each year] for the rest of my career, I'll be happy."

Johnson will play rounds one and two in Hawaii in the company of Bryson DeChambeau, who has stated his intention to putt with the flagstick in following a rule change that allows players to do so when they are on the green.

"It's gonna be weird. The flag's gonna be going in and out a lot, but it's alright," said a grinning Johnson. "I guess I will leave it in occasionally."