Frenchman Julien Guerrier opened up a one-shot lead after the opening day of the Andalucia Masters as world number one Jon Rahm equalled his worst ever round at a European Tour event.
Guerrier battled the wind brilliantly at the notoriously difficult Valderrama to card a 67, 11 shots better than Rahm, who was in a tie for 107th at seven over.
The US Open champion now faces a fight just to make the cut in his second consecutive event on home soil after finishing in a tie for 17th as two-time defending champion at last week's Acciona Open de Espana.
Guerrier's time in Spain has been more fruitful, with the 36-year-old claiming a top-three finish last week to virtually assure his place on Tour next season.
He carded six birdies and two bogeys to get to four under on day one at the 1997 Ryder Cup venue and admitted he was enjoying playing with less pressure on his shoulders.
"I think I'm more relaxed," he said. "I'm playing to shoot a low score, not save my card, that's the main thing. We work every day, improve our game and it's working at the end of the year.
"It was really complicated today. The wind was growing stronger on the back nine.
"I had two bogeys on the score card, very few, and six birdies. It's good to have six birdies in these conditions."
Last week's winner Rafa Cabrera Bello was his nearest challenger at three under, a shot clear of Frenchman Romain Langasque.
Ireland's Jonathan Caldwell is five shots off the pace after a mixed round of 72 left him on +1.
