KOHLER, United States (AFP) - Two major triumphs in one year and a shot at the world No. 1 have Jordan Spieth rapidly recalculating his career goals.

Heading into the PGA Championship that tees off at Whistling Straits on Thursday, the 22-year-old Masters and US Open champion is closing in on top-ranked Rory McIlroy much sooner than his meticulous career plan forecast.

"I did not have a timeframe set for that," Spieth said of reaching number one. "Given everything that's happened, I believe now that I would like it obviously to be sooner rather than later - and then to be able to hold on to it," he said.

"As I'm sure Rory knows, Adam Scott knows, Luke Donald knows, there's Tiger," he said. "There's a number of them that understand what it's like. I don't know what that feels like - yet."

Spieth earned his first major title in historic style at Augusta National in April, deftly handling the final-round tension to hold off Phil Mickelson and Justin Rose to win the Masters by four shots.

He edged fellow American Dustin Johnson for the US Open title at Chambers Bay, to arrive at storied St. Andrews with the third leg of a possible calendar grand slam in his sights.

"Of course, after winning the first leg - let alone the first two legs - that talk, that noise, starts to come about, but it's still a whole other animal just to win a major in general," Spieth said.

"I wasn't coming (to the British Open) trying to win a grand slam. I knew the history of it. I knew what we possibly could have done.

"But at the same time, my frustration was only that we were tied for the lead with two holes to go - with one of them being a birdie hole - and we didn't close it out. We didn't even get into a playoff."

That disappointment has fuelled Spieth's appetite for a PGA Championship win even more than the knowledge that he could join Ben Hogan and Tiger Woods as the only golfers to win three major championships in the same year.

But he's not getting ahead of himself. Before he can even hope to hoist the Wanamaker Trophy he'll have to scratch one more thing off his original 2015 to-do list - making the PGA Championship cut for the first time.

"I still haven't accomplished that goal," said Spieth, who missed the PGA Championship cut in 2013 and 2014.

"I've got some work to do these first two days, and from there we'll adjust and work our butts off to try and get a third major this year - which would be a pretty cool place in history to be a part of."