Jordan Spieth, at 20, is sitting on top of the golf world

AUGUSTA, Ga. — The man with the most continually shouted first name in golf will begin the final round of the Masters on Sunday in a final pairing with the most frightening of competitors.

A 20-year-old kid who refuses to call him by his first name.

Jordan Spieth respectfully refers to all of his elders as “Mister,” which will make him the only person at Augusta National not referring to his co-leader as “Bubba.”

“Yeah, ‘Mr. Watson,’ for sure,” Spieth said, pausing, smiling. “Just because it’ll mess with him.”

He’s messing with everyone, this kid who looks as if he should be howling from a Cancun balcony on spring break instead of shooting a two-under-par 70 — while Watson was shooting a 74 — to tie the 2012 Masters champion for the lead entering Sunday’s final day.

When told he would be addressed like an old man for his next four hours of golf, Watson returned the smile.

“That’s fine — when I’m hitting it past him,” he said.

It’s going to be quite the duel, Bubba against bubble gum, a green jacket against a greenhorn, Iceman against Maverick. When the tournament began, some worried that with no Tiger Woods in the field, there would not be a main attraction on the final day.

Turns out, there are two of them, and although they sit atop a leaderboard that features 11 other guys within four strokes, it’s going to be hard to watch anyone else.

If the baby-faced Spieth triumphs, he will be the youngest winner in Masters history and the first golfer to win this tournament in his first try in 35 years. If the weary-looking Watson wins, he will be only the eighth golfer to win two Masters in a three-year span.

It’s a standoff that couldn’t wait for Sunday, actually beginning early Saturday evening in the interview room, starting with the “Mister” messing and picking up steam.

“Tomorrow is about seeing how I can control my game and emotions out on the golf course against guys that have even won here recently,” Spieth said. “Doesn’t necessarily mean, I don’t think, that they had an advantage in any way.”

Bubba Watson doesn’t have an advantage in that he pulled off a dramatic win here just two years ago? Watson sighed.

“He’s young, nerves are no big deal to him,” said Watson. “I’ve won one, so I’ve got that going for me.”

As if one couldn’t already tell, they have arrived in this same revered place from very different directions.

Watson began the round with a three-stroke lead, stretched it to five after two holes, then lost it all in about an hour. The likable guy with the baggy shirts and booming drives had talked earlier in the week about having finally overcome the expectations that accompanied his 2012 Masters win, yet, all at once, he seemed to again be swallowed up in them.

His swings were tight. His putts were short. He had five bogeys, he had two three-putt greens after going 250 holes without a three-putt, he lost all momentum, and only a saving par putt on the final hole kept him from losing the lead.

“We are all going to be nervous and we all know what it means to our career,” Watson said. “So it’s going to be tough for everybody, not just the guys that have never won one.”

Although there is nothing more exciting than growing Augusta cries of “Hey, Bubba!” there perhaps is nothing more disheartening than what happened when those cries faded Saturday into a gaggle of muted “Oh, Bubba.”

“We didn’t hear anything,” Michael Greller, Spieth’s caddie, said with a grin.

Of course they didn’t. The kid from Dallas entered this tournament already confident in his anointment as golf’s next great thing. He grew up dreaming about playing in the Masters, and actually persuaded his parents to allow him to change the lawnmower settings for a patch of frontyard grass that he would cut into a fake Augusta green. He and his friends were even scolded at his local country club for shouting on the putting green, “This one is for the Masters!”

“You just dream of what it would mean and how cool it would be,” Spieth said.

That dream was launched with his first pro event little more than a year ago, and he has already won once and made nearly $4 million. At an Augusta house he is sharing with — who else? — his parents, he can rest his head Saturday and seriously dream that Masters dream again. He made four birdies and two bogeys Saturday even as defending champion Adam Scott played next to him and Watson played behind him. With safe approaches and precision putting, he turned this old-style tournament into a regular Spieth-easy.

“It’s incredible, a brand-new experience; it kind of feels like we’re playing with house money,” caddie Greller said. “We’re too dumb, maybe, to know where we’re at.”

At times, Spieth charmingly acted as if he were at the local public course, loudly scolding himself or directing his shot. He would shout, “Sit down, sit down!” while actually crouching down. He would wave his hand and holler, “Kick left one time!” Occasionally he would just duck his head and moan, “C’mon, Jordan.”

Spieth calmly explained himself, saying, “I’m 20 and this is the Masters and this is a tournament I’ve always dreamt about and, like Mr. [Ben] Crenshaw has always said, it brings out more emotion than ever in somebody.”

Greller laughs. What can he say? It’s like the kid told everyone. Twenty!

“There’s a lot of monologue, there’s a lot of dialogue too,” Greller said. “I taught sixth grade for 10 years, I’m a very patient person. I Iearned with Jordan, he just needs to be heard.”

Consider it done. The sports world is listening. Mr. Watson, and history, are waiting.

bill.plaschke@latimes.com

Twitter: @billplaschke