ST LOUIS (AFP) - Three-time major champion Jordan Spieth says going winless for more than a year has him "under the radar" as he seeks a Career Grand Slam by winning the 100th PGA Championship.

The 25-year-old American hopes to join legends Tiger Woods, Jack Nicklaus, Ben Hogan, Gary Player and Gene Sarazen in having won all four majors at least once.

But eighth-ranked Spieth, the 2015 US Open and Masters winner, has not won a title since last year's British Open.

"I feel somewhat under the radar this year," Spieth said.

"Getting in the winner's circle when it has been over a year is something I would like to do, but I don't feel any added pressure.

"If it happens or doesn't happen through the rest of this calendar year, I'm working in the right direction. I'm doing the right things and (if) you get yourself in position enough, the bounces will go your way."

Spieth, who shared 28th at last year's PGA Championship in his first chance to complete the Career Slam, says he was more nervous about his chance to make history last year when his Claret Jug win was fresh.

"I was probably a little more anxious last year. There was a big focus on it, given it was right after winning the Open Championship," he said. "I was in form, and going to a place that, if I worked up the leaderboard, it would create a lot of noise."

That would be the same this week at Bellerive, where Spieth has family ties through a maternal grandfather. But it would be true wherever and whenever the PGA is played.

"This tournament will always be circled until I'm able to hopefully win it some day to complete the career Grand Slam, which will ultimately achieve a life-long goal for me," Spieth said.

"So certainly emphasis in my head on it, but nothing overpowering, nothing that takes over once I start on the first tee, just more going into the week.

"If I were to get myself into contention this week or next year or whatever, I don't think that plays any part in forcing anything. I'll approach it as this is a golf tournament I have a chance to win, go about how you go about any other Saturday and Sunday trying to win."

SUNDAY 'BRIGHT SPOT'

So much for staying under the radar.

"After one round it changes," Spieth said.

"Ideally going into Sunday you're a bright spot. You're not under the radar. So first and foremost is trying to be in form.

"If I don't have a chance to win on Sunday, I'm disappointed waking up. But I understand this year has been kind of a building year for me and I've been working back towards the level I like to be at, and it's getting close and certainly starting to see some results from it."

Spieth has finished in the top 10 in nine of his 23 career major starts, including second in the 2015 PGA Championship, third in this year's Masters and tied ninth in last month's British Open despite a birdie-less final round 76.

"If you put yourself in the position enough times, you're going to have some go your way and some that don't," said Spieth.

"And it's easier to accept if that's the way you look at it."