Jordan Spieth struggled on the 18th green and will take just a one-stroke lead into Sunday at Augusta. (Harry How/Getty Images)

This has been a week of strange sights at Augusta National — of viral six-putts that made grown men wince, and once-a-decade gales that frayed nerves and blew stationary golf balls into creeks. There is even a 58-year-old man here who thinks it is still 1985. But there was also an underlying sense of sameness and logic, because Jordan Spieth was in command of the Masters, and no manner of challenger — human, meteorological or otherwise — seemed capable of altering that.

And then came two wayward swings of Spieth’s driver on his final two holes Saturday afternoon, and now, no one can say with any degree of certainty what Sunday might bring.

The resulting bogey at 17 and double-bogey at 18 by Spieth have turned Sunday’s final round from what was setting up to be a second straight coronation for the 22-year-old defending champion into what could be a long, compelling slog, with all sorts of intriguing characters chasing him.

Instead of a steady 70 and a four-shot lead entering Sunday — the same margin he led by a year ago, when he won his first green jacket in dominant fashion — the two blocked drives had Spieth limping home with a 1-over-par 73, good for a 54-hole score of 3-under 213 and just a one-shot lead heading into the final round.

“I just have to absolutely throw this [round] away,” a dejected Spieth said. “Just pretend everyone’s tied. Just think that this is the position I wanted to be in after 54 holes and not think about the finish to the round.”

Spieth will be paired Sunday with a surprise contender — Smylie Kaufman, a 24-year-old PGA Tour rookie playing in his first Masters and just his second major championship, and who shot the day’s best round, a 69, to finish just a stroke behind Spieth, his friend and former junior-golf tormenter.

“He’s probably 1,000-0 [against me]. He’s always beating me,” Kaufman said of Spieth. In regards to his first time in contention on such a stage, Kaufman said, “I know what’s going on. I know it’s the Masters. I know how important it is. But I’m just going to go out there and just do my best. I think that’s all I can do tomorrow, and just not try to force it and just try to have some fun.”

Two shots back of Spieth, at 1-under 215, are the only other two players under par through 54 holes — 24-year-old Japanese phenom Hideki Matsuyama and a man who hasn’t seen 24 in nearly 31/2 decades.

Bernhard Langer is 58 years old. The native of Germany won his two green jackets in 1985, when the Berlin Wall still stood, and in 1993, when, over in Texas, Chris Spieth was six months pregnant with a boy who would be born July 27 and named for his father’s favorite basketball player.

“It would be one for the old guys,” said Langer, 12 years older than Jack Nicklaus was in 1986 when he became the oldest in history to win the Masters.

But Spieth’s late stumbles Saturday — when he pushed a pair of drives way right, forcing awkward recovery attempts that ultimately failed — also opened the door to a group of talented fellows for whom the championship might have otherwise been out of reach.

They include Jason Day (71), the world’s No. 1-ranked player and the pre-tournament betting favorite; Dustin Johnson (72), whom Spieth outlasted to win the U.S. Open last June; and England’s Danny Willett, the 12th-ranked player in the world. All sit at even-par 216, three shots back of Spieth.

Even four-time major champion Rory McIlroy, who played his way into Saturday’s final pairing with Spieth, only to implode spectacularly with an adventure-filled 77 that included not a single birdie, remains in contention, thanks to Spieth’s unexpected generosity on the day’s final two holes.

“To be honest with you, I would be feeling a lot worse about myself if I hadn’t just seen what Jordan did the last two holes,” McIlroy said. “I sort of take a bit of heart from that — that I’m still in this golf tournament.”

The weekend’s possibilities had golf fans salivating, with the prospect of Spieth and McIlroy dueling for at least 18 holes and perhaps 36. The Masters had never seen a weekend matchup like this in the final pairing, with two such young and accomplished golfers — multiple major-winners under the age of 27 — squaring off.

They shook hands on the first tee Saturday afternoon, and anyone who cared to examine them side by side could note the differences. Spieth made nervous small talk with his caddie. McIlroy leaned on his golf bag and looked around. Spieth wore sensible clothes. McIlroy’s half-zip sweater was so tight, it may have been the only bit of textile in the vicinity not blowing around in the wind. Spieth had his yardage booklet in his left back pocket, McIlroy in his right.

But by the 11th hole, as McIlroy went from the pine straw to the water for a double-bogey to fall to 5 over for the day — with more than one onlooker reminded of his infamous Sunday meltdown in 2011 — any semblance of match play between the two young champions was gone. It wasn’t as if Spieth was playing so much better, tee to green, but he kept pouring in six- and eight-foot putts, whether for birdie or par, while McIlroy couldn’t buy one.

“I turned around after 15 and said, ‘How the hell is he 2 under par today?’ ” McIlroy said of Spieth. “But [his putting is] his most impressive asset. As much as it could be annoying to his competitors, it’s very, very impressive.”

Climbing as high as 6 under — with birdies at 12, 14 and 15 — and with a lead that stretched as high as four at one point, Spieth’s last remaining challenger down the stretch Saturday was himself. And it proved to be tougher than all the others. On his tee shot at 17, in particular, he thought hard about hitting 3-wood but talked himself into the driver.

“It should not have been a tough decision,” he said. “I was feeling maybe this should be [a] 3-wood, and when that feeling comes up, you should never then step back up with a driver.”

And so, for the seventh straight round in the Masters, Spieth is the outright leader, a distinction no other golfer in history can claim. But thanks to the mess he made in the long shadows Saturday evening, for there to be an eighth — and a second green jacket to go along with it — Spieth will have to earn it the hard way.