As the shadows grow longer Sunday evening over Atlanta Athletic Club, someone at the PGA Championship will step to the 15th tee with an advantage, and need simply to survive. It may be obscure third-round leaders Brendan Steele or Jason Dufner, or any of the 17 other players within six shots of the lead. The season’s final major, to this point, has been difficult to define, because only true golf insiders know the characters in and around the lead. But it’s hard to imagine that the tournament won’t ultimately be defined by a savage, unforgiving four-hole finish.

“I don’t think there’s another stretch that I can remember that’s this difficult coming in,” said Tiger Woods, long before he missed the cut.

First, those who will try to navigate it: Steele, a 28-year-old Californian, had never played a PGA Tour event before this season, and this is his very first major championship. He is ranked 121st in the world. He won the Texas Open earlier this year, a turn of events that he said “kind of blew my mind.”

Dufner is a 34-year-old who walked onto the golf team at Auburn and has won nothing this side of the minor-league Nationwide Tour. He lost in a playoff in February in Phoenix, sits 80th in the world rankings and has missed so many recent cuts that, before this week, he hadn’t played a competitive round on the weekend since May. He could take his chubby face and waggling swing onto any municipal driving range anywhere in the country, whack a bucket of balls, and walk out unnoticed.

“Might make me a little more relaxed knowing that everybody is kind of in the same boat struggling with those emotions and thoughts and the mentality of trying to win a major,” Dufner said. “But I just feel like if you’re playing good, you should be confident.”

Both those men — Steele behind his 66 Saturday, Dufner with a 68 — are at 7-under-par 203 through three rounds. The pack that trails is hardly star-studded. Keegan Bradley, a PGA Tour rookie who also won earlier in the season in Texas, trails by a shot after Saturday’s 69. Scott Verplank, the 47-year-old veteran from Oklahoma, is two back. Steve Stricker, as polite a person as anyone would ever want to meet, brings what amounts to star power, though its doubtful the majority of those in the sweat-soaked galleries here could recall that he is the highest-ranked American in the world, at No. 5. He sits three behind.

“A lot of first-timers up at the top,” Stricker said. “I don’t know how far back you’ve got to go to find a major champion winner there.”

That would be to David Toms, the 2001 PGA champion right here, and Charl Schwartzel, who won the Masters this past April. Both are tied for eighth. But Stricker’s point is well-taken. The only other major champions inside the top 30 are Jim Furyk, six back, and Phil Mickelson, seven behind.

So whoever steps to the 15th tee with the lead Sunday — be it Steele or Bradley, in their first major, Dufner in his 11th or Stricker in his 50th — will have to deal with his own nerves, a new situation and an unrelenting stretch.

“You’re really going to need to commit to the shots that you’re hitting,” Steele said. “Any sort of wishy-washy-type play there is not going to get it done.”

Go to the scorecard. The 15th is a par 3 of — and this is not a typo — 260 yards. With a large bunker to the left. And another to the back right. And that’s if you carry the water that guards all but the very left portion of the green. Earlier in the week, Mike Small, the only club pro to make the cut here, told Stricker, his old college teammate at Illinois, that the hole is a dogleg par 3.

“It’s too long,” Stricker said. “It doesn’t need to be that long.”

Among the victims Saturday, when the tees were pushed forward to a mere 223 yards: Furyk, the 2010 PGA Tour player of the year who was around the lead all day — until he dunked his tee shot there. He made double bogey to drop from 5 under to 3 under.

That hole just starts the fun. The 16th is an uphill, 476-yard, dogleg right par 4 with two greenside bunkers, each the size of a small county. The 17th is, in some senses, the breather, a par 3 of “only” 207 yards. But it is entirely over water, there are bunkers in the back, and the field has made 32 scores of double bogey or worse.

Then there is the finishing hole. On the scorecard, it lists at 507 yards — and is a par 4. Saturday, it played a mere 484 yards, but water still guards the entire left-hand side; bunkers dot the right.

“It’s a tough hole,” Toms said. “And I’m not afraid to lay up.”

He did just that to win in 2001, making par. Others might have been advised to do so this week. World No. 1 Luke Donald made double bogey there Saturday to fall to 1 under. Mickelson has played the first 17 holes in 4 under, and at No. 18 has made double bogey, bogey and bogey.

Furyk, too, took himself almost completely out of contention by roping his drive into the water, dropping, then finding the water again. For the week, he is 6 under on the first 14 holes, 5 over on the final four holes.

Saturday evening, Steele set up what might happen in the final round. He came to 18 leading Dufner and Bradley by two. He found a bunker off the tee, laid up, and made bogey. Instead of having the lead to himself, he fell back to the pack.

“This course is pretty stressful,” Dufner said. Nowhere more so than those final four holes, the holes where the year’s final major will be decided.