Rahm, who is currently sitting atop LIV's individual rankings with a win and three runner-up finishes in five events, looked dejected as he made his way around Augusta National while carding a birdie-less six-over-par 78 that left him searching for answers.
"It's a hard golf course," Rahm said on the layout where he won the 2023 Masters. "Some of the players might have been able to manage a respectable round, but when you have no feel with the swing whatsoever, it's just not an easy one."
The two-time major champion had four bogeys by the time he reached the turn and then ran into trouble at the par-five 13th, where he turned a potential birdie into a double-bogey.
Rahm sent his approach shot from 176 yards into the azaleas, but was unable to find his ball. After taking a drop, he chipped to within 32 feet of the cup and then needed three putts from there to find the hole.
"I still don't know what happened, honestly," Rahm said about his second shot at the 13th. "To get so lucky off the tee, to have an eight-iron in my hand, I don't know, that ball came out 20 - about 10 yards left, 20 feet higher, and hooking in a way that I didn't expect.
"To make such a mistake from what could have been a good birdie look, it's a big problem. It's probably the part I'm the most upset at today."
Of the 10 LIV players in the starting Masters field of 91 golfers, Rahm came into the week as one of the ones considered to have the best chance. He finished the first round in a share of 73rd place and 11 shots back of co-leaders Rory McIlroy and Sam Burns.
Despite the disappointing start, Rahm knows there is plenty of golf left and knows a thing or two about bouncing back at Augusta.
In 2023, he opened the tournament with a four-putt double bogey but quickly turned things and slipped into a Green Jacket later that weekend. Last year he opened with a three-over 75 before finishing in a share of 14th.
"I've done that a few times," Rahm said about his ability to bounce back from slow starts at the Masters.
"But it still sucks to be in this position, to need a Herculean effort the next two days to give myself a chance to maybe sniff having a chance to win. It's just frustrating."