The US Open at Oakmont Country Club proved to be a formidable challenge for many, including Rory McIlroy, who struggled after a promising start. McIlroy, who had a strong opening with two under through nine holes, faltered with four bogeys and a double bogey, finishing with a four-over 74.

JJ Spaun, who McIlroy defeated in a playoff at The Players Championship earlier this year, led the field with an impressive four-under round. Spaun's performance was marked by four birdies in his first eight holes, maintaining a bogey-free round through the first half of the day.

Other notable performances included Thriston Lawrence from South Africa, who was just one shot behind Spaun, and Kim Si-woo from South Korea, who finished two under. Thomas Detry of Belgium and Ben Griffin of the USA both ended the day one under par.

Defending champion Bryson DeChambeau and world number three Xander Schauffele both had mixed rounds, with DeChambeau posting a 73 and Schauffele a 72. World number one Scottie Scheffler was among the players scheduled to start later in the day.

The course at Oakmont, known for its difficulty, lived up to its reputation with more bogeys than birdies recorded in the morning wave. As the course dries out and greens become faster, the challenge is expected to intensify.

McIlroy, who has finished runner-up in the last two US Opens, will need to improve in the second round to stay in contention. His past performance at Oakmont includes missing the cut in 2016, adding pressure to his current campaign.

As the tournament progresses, all eyes will be on the leaders and whether McIlroy can overcome the challenges of Oakmont to claim his second US Open title.