As Bryson DeChambeau and Rory McIlroy made slow starts to their US Open title challenges, JJ Spaun continued his career-changing season by grabbing a history-making lead.

Spaun set the clubhouse target with a stunning four-under 66 on Thursday morning, where he carded the only bogey-free round of the day and equalled the best start to a US Open at Oakmont Country Club.

There were zero bogey-free rounds in 2007 at Oakmont and Dustin Johnson was the only player to manage it during his victory here in 2016, while Spaun’s impressive start – in a wave where only five players finished under par – was the first bogey-free round of his major career.

“I kind of came out here with no prior history at Oakmont, not really knowing what to expect even US Open-wise,” Spaun admitted. “This is only my second one. I don’t know if that freed me up in any aspect, but I just tried to take what the course gave me.

“I hit a lot of good shots and tried to capitalise on any birdie opportunities, which aren’t very many out here. But I scrambled really well, too, which is a huge component to playing well at a US Open, let alone shoot a bogey-free round. I’m just overly pleased with how I started!”

Spaun’s hot start was one shot better than closest challenger Thriston Lawrence after the morning wave, with DeChambeau seven strokes back after an opening-round 73 and McIlroy a further shot behind after dropping six shots in an eight-hole stretch.

Is Spaun’s fast start a surprise?

A chip-in at the par-four 10th – his opening hole of the day – was one of four birdies for Spaun, who scrambled brilliantly and converted six putts from par of seven feet or longer during his first round.

Spaun has never posted a top-20 finish in a major and is without a PGA Tour title since the 2022 Valero Texas Open, his only victory to date, although he has jumped from outside of the world 100 to inside the top 25 after an impressive start to the season.

“JJ Spaun is a really good player and is a guy who is improving every year on the PGA Tour,” former Ryder Cup captain Paul McGinley told Sky Sports. “He’s trending well, with two seconds and a third place this year, so this is not a springer out of nowhere.

“This a good player who is having a really good season. He kept the ball in front of him, which is important, and didn’t leave himself shots into trouble. He putted magnificently and was one of the best putters during his opening round.

“He’ll hang around and I don’t think he’s going to fall away from the leaderboard, just like he did at TPC Sawgrass when he pushed Rory McIlroy right to the line and into a play-off.”

‘I’ve been consistently there’ – Spaun’s season so far

Spaun took a one-shot lead into the final round of the Sony Open in January, where a penultimate-hole bogey and closing par on a par-five left him in tied-third and one shot outside of the play-off.

He finished tied-second a few weeks later at the Cognizant Classic, having carded a bogey-free 66 on the final day, before a brilliant performance at The Players saw him drag McIlroy into a Monday play-off.

Spaun held a 54-hole lead at TPC Sawgrass and recovered from a mid-round wobble to birdie two of his last four holes, taking him into a play-off when McIlroy blew his late lead, but a triple-bogey on the second extra hole ended his hopes.

The American also made strong starts with opening rounds of 66 and 67 respectively at the RBC Heritage and Truist Championship, both Signature Events on the PGA Tour, while he made a 66-68 start on his way to a tied-sixth finish at the Charles Schwab Challenge.

“I’ve been consistently right there,” Spaun said. “Everyone knows that the more you put yourself there, the better you’re going to have results and the better you’re going to play, then eventually turn one of those close calls into a win.

“The Players was a kind of spring into the self-belief because it wasn’t like I faked it. You can maybe fake it at the Sony and Cognizant or whatever, but to do that at The Players, a course where I’d never done well historically…

“To go head-to-head with Rory on Sunday, and then the play-off was great for my confidence. Unfortunately, I didn’t win, but it was great for me to kind of lean back on that experience and know that I can perform on the biggest of stages and handle it with the pressure.”

‘I have nothing to lose’ – could Spaun claim maiden major?

The last three US Open winners at Oakmont opened with a round under-par, while 23 of the last 26 US Open champions were within four of the lead after the opening day, with Spaun ready to build on his start and early-season form and challenge for a maiden major title.

“It definitely makes me feel good, makes me feel confident that I’m leading the tournament,” Spaun added. “But yeah, there’s plenty more golf left and this course is only going to get tougher.

“I just think I’m trying to feel like I have nothing to lose. That was kind of my mantra at The Players when I was playing really well at that tournament and going into Sunday with the lead. It was like, I feel like I have nothing to lose.

“So I’m going to roll with that again this week, and hopefully it’ll turn out more in my favour.”

Who will win the US Open? Watch throughout the week live on Sky Sports. Live coverage continues on Friday from 12.30pm on Sky Sports. Get Sky Sports or stream no contract on NOW.