(Photo credit: Bill Streicher-Imagn Images)

NEWTOWN SQUARE, Pa. -- The PGA of America may have opened up the setup at Aronimink Golf Club, but that did not open up the crammed PGA Championship leaderboard Saturday.

Alex Smalley rallied on the back nine to shoot a 2-under-par 68 and build a two-shot lead, but nearly two dozen golfers are in striking range after the third round of the second major of the year.

If Smalley were to lift the Wanamaker Trophy on Sunday night, it would mark one of the biggest upsets in recent major golf history. Smalley, 29, is playing just his fifth major and has never finished better than T23. The Rochester, N.Y., native also has yet to win a PGA Tour event in 140 starts.

He enters the final round at 6-under 204, separating late in the day from a new group of contenders at 4 under par: Spaniard Jon Rahm (67), Englishman Aaron Rai (67), Sweden's Ludvig Aberg (68), Germany's Matti Schmid (65) and Canadian Nick Taylor (65) -- all of whom made mid-afternoon moves despite increasing winds.

Three major winners are three shots back at 3 under: Northern Ireland star Rory McIlroy (66), Xander Schauffele (66) and Patrick Reed (67). Joining them is Maverick McNealy, who shared the 36-hole lead with Smalley but bogeyed two of his last four holes to stumble to a 71.

The conditions were far more scorable Saturday morning than at any point of the first two rounds. Chris Kirk, Englishman Justin Rose and Norway's Kristoffer Reitan took advantage with rounds of 65 after only one 65 was seen Thursday or Friday. That trio rose to 2 under for the championship, as did Germany's Martin Kaymer (66), Chile's Joaquin Niemann (66), Bud Cauley (67), Ben Griffin (67) and Aussie Cameron Smith (68).

Also in the 12-way tie at 2 under are Max Greyserman, Chris Gotterup, Japan's Hideki Matsuyama and Australia's Min Woo Lee, each of whom settled for 71s after starting the day one behind the leaders.

Smalley appeared to take himself out of the picture when he bogeyed three of his first four holes. He quietly worked his way back by posting birdies at Nos. 7, 9 and 10 with a bogey speed bump at No. 8.

Smalley and McNealy each birdied the short par-4 13th to return to 4 under. Then Smalley holed a 27-foot putt straight uphill at No. 15 to take the outright lead before adding another birdie at the easy par-5 16th. He became just the second player to touch 6 under this week as McNealy spent a brief time at that score Friday.

Smalley couldn't get up and down from a bunker at the par-3 17th, but saved par to maintain the lead. Then came a 14-footer for birdie at the last.

--Adam Zielonka, Field Level Media