The leaderboard was spinning like a tombola at Aronimink on Saturday, where at one point or another just about every player in the field had a birdie putt to take a share of the lead and then a bogey putt to let go of it again. When the drum finally stopped turning, Alex Smalley, a 29-year-old from North Carolina who has never won a professional golf tournament, was top of the leaderboard on six under, two shots clear of a five-way tie for second. No disrespect to Smalley, the world No 78, but the field are queued up like bowling balls on the rack waiting to take a run at him on Sunday.

Philadelphia loves an underdog, but it’s probably best if the trumpeter waits another day before he strikes up the opening notes of the Rocky theme.

There are 21 players within four shots of a share of first, and eight major champions among them. Jon Rahm, who has finally rediscovered his major touch, is in the group closest behind him on four under, and Rory McIlroy, Xander Schauffele and Patrick Reed are all only one further back than that. It doesn’t stop there. Justin Rose, Martin Kaymer, Cameron Smith and Hideki Matsuyama are grouped on two under. Even Scottie Scheffler, whose stone-cold putter cost him a handful of birdies, may still fancy his chances from five shots off Smalley’s lead.

It is the most congested major leaderboard anyone can remember. “I’ve never seen anything like this,” Scheffler said. “I’ve never seen a leaderboard this bunched up. It’s quite literally anybody’s tournament.”

Smalley was playing in the final pair, along with Maverick McNealy, and until he pulled clear by making a birdie on the par-five 16th, he was part of a six-way tie for first place. It would have broken the record going into the final day in a major, beating the five-way tie at the Open at St Andrews back in 1933. Instead Smalley’s out in his own. It is the first time in his life he’s had the 54-hole lead in a professional tournament. “I don’t like being in the spotlight a whole lot,” he said on Friday night. “I’m still trying to get used to playing in front of large groups of people like there are at tournaments like this one.”

He seems to be catching up with it. He played a hell of a round on Saturday. He looked all but out of it after he scored four bogeys in his first eight holes, but then he went and played the next 10 in five under.

As well as Åberg and Rahm, the group of five immediately behind him included England’s Aaron Rai, who managed to hold on to his score at five-under through the late afternoon until he made a dreadful mess of the 18th, when he veered from the rough on the left to a bunker on the right. It’s been more than 100 years since an Englishman won this tournament, and Rai, 31, has a shot at breaking one of the longest jinxes in major golf. But it’s awful busy up there at the top. By mid-afternoon it had got so bunched up there that a lot of the players admitted they had given up looking at the leaderboards.

“It’s so bunched it was kind of pointless,” said Canada’s Nick Taylor, also on four under, and besides, the greens here are so mean you couldn’t afford to take your eyes off them long enough to take it in.

So a tournament that has been widely criticised by the players for being so damn difficult may yet end in one of the more extraordinary Sundays in major history. It helped that the sun was out and the wind had shifted so that some of the greens on the shorter par-fours were reachable off the tee, but it was true, too, that after all the criticism they received from McIlroy and Scheffler about the fiendishly difficult pin positions on the first two days, the tournament committee were a little more generous with their setup.

On Friday, Scheffler had described the pins as “absurd”, and McIlroy had said they were “not great”. After scoring 66, the Northern Irishman explained that he was just venting his pent-up irritation.

“When you have a set of greens like this, you can start to frustrate people pretty easily,” McIlroy said. “You heard it in me last night, you heard it in Scottie. There was a lot of guys that were frustrated yesterday coming off the course. But at the same time, it creates a hell of an entertaining championship. If I wasn’t playing this tournament, I’d love what’s going on this week, but watching and playing are two different things.”

He was in a better mood on Saturday. “No profanity today,” McIlroy said as he walked in to talk to the press. Two days on from his “shit” performance in the opening round, when he made four back-to-back bogeys and was tied for 105th, McIlroy is right back in contention. “I’ve climbed my way out of that hole and I’m proud of myself for doing that,” McIlroy said. “There’s one more day left, and I feel like I’m close enough to the lead that I’ve still got a good chance.” Him, and just about everyone else holding a club.

“It is,” Schauffele said, “going to be an absolute free-for-all.”