The notoriously unpredictable weather conditions and the lack of a dominant force in golf just now means picking a winner at this weeks British Open is impossible in the eyes of

The 23-year-old world number three became a golfing superstar in 2015 when he won the Masters and US Open in quick succession.

But since his double triumph two years ago, eight subsequent majors have yielded eight separate winners, underlining how much competition there is at the top of the sport.

And there are plenty of contenders to keep that run going this week, including Spain's Irish Open winner Jon Rahm and Englishman Tommy Fleetwood.

That is why Spieth says recent talk of a 'Big Four' comprised of him, Dustin Johnson, Rory McIlroy and Jason Day is already redundant.

"I think you look at a guy like Jon Rahm, how does he deserve not to be in a conversation like that? What he just did at the Irish Open and what he has been able to do this year, he did it two weeks ago at links golf. He destroyed the field," Spieth said at Birkdale on Tuesday.

"I don't think he would have been someone that you would put there if you were about to name four guys.

"I don't know what's better for golf, (but) from my opinion it's very exciting when you've got to beat that many great players with that much confidence.

"It could be anybody this week," added Spieth, who came fourth at St Andrews two years ago and is wary of how big a part luck plays in terms of the weather.

Conditions were glorious on Tuesday, but the forecast is gloomier heading into the weekend.

"Most of the time there's at least a group that gets the worst weather. And it's almost impossible to win in that circumstance at an Open Championship.

"So nothing you can do about that other than keep your head down, play as well as you can, and see what happens after two days."

Spieth will play with reigning champion Henrik Stenson and Kim Si-Woo in the first two rounds. He arrived in England fresh from winning the recent Travelers Championship to claim his 10th US PGA tour title and his second of the year.

"I've struck the ball better than I did in '15," he said when asked if he was a better player now than two years ago.

"If I putted the same as '15 I'd be having a better year right now. So, yeah, certain parts of the game I think I've improved on. And others, you know, it's just fluctuated," added the Texan, who is in his fifth season as a professional.

"I recognise that being five years in now, and five years doesn't make me a veteran, but it helps me realise kind of how things go. And last year I was pretty caught in 2015, and this year I'm not."