"It was a tough round. I was never comfortable," said a dismayed Rahm after his poor opening at Valderrama on Thursday.

"I don't want to go home on Saturday, and if somebody can overcome this it's me. But I don't have any more room for error."

Rahm had four bogeys and a double bogey on his front nine and another bogey on his back nine at the celebrated Real Club Valderrama course in southern Spain.

"It's frustrating because this is a course that I like. With this wind the course becomes very difficult."

U.S. Open champion Rahm was coming off a disappointing 17th place finish at the Spanish Open last week on his return home after nearly two years.

He opened with a 63 but had lacklustre rounds the rest of the way and was not in contention to defend his title on Sunday. He'll now need a good second round just to make the cut.

It was his worst round since he also shot 78 in the second round at The Open in 2018, while the worst score of his career was his 82 in the third round of The Players Championship in 2017.

He finished the day in a tie for 108th, with only 10 players shooting higher scores than him.

Julien Guerrier, who finished in a tie for third at the Spanish Open, was the first round leader after a four-under 67, while Spaniard Rafa Cabrera Bello, winner at the Spanish Open, was one shot behind.

Jason Scrivener and Min Woo Lee were the best of the Aussies, the pair of West Australians sharing 39th, six shots back of Guerrier.