Englishman Lee Slattery leads the field after the opening day of the Wales Open in Newport on Thursday, while Australian Marcus Fraser made a positive start.
Slattery fired five birdies in his four-under-par 67, giving him a one-shot advantage over German Marcel Siem and Tim Sluiter of the Netherlands.
A group of four players are a further shot back after an exciting first day at the Celtic Manor Resort.
Slattery, who this week qualified for his maiden US Open, started well with a birdie on the second and he made up further shots on holes five and eight.
A bogey on the ninth threatened to derail his round but he responded strongly with birdies on the 11th and 12th.
And the 33-year-old avoided further blemishes on his run home to finish with an impressive round of 67.
"I know Olympic Club is going to be difficult, but I'm really looking forward to it," said Slattery on his visit to San Francisco for the US Open.
"It's more the atmosphere. I remember The Open at Hoylake (his only previous major was there in 2006) and I thrived on it."
Siem was slightly more erratic, hitting six birdies and three bogeys while a double-bogey on the par-three 17th cost Sluiter a chance of holding the outright lead.
Sluiter made a superb start, hitting six birdies on the first 10 holes and was made to rue his late error.
Spanish duo Gonzalo Fdez-Castano and Pablo Larrazabal, Sweden's Joel Sjoholm and Simon Thornton of the Republic of Ireland are all tied for fourth at two-under.
A further shot back are Fraser, Scotland's Steven O'Hara, Englishman Ross Fisher and Paraguay's Fabrizio Zanotti in a tie for eighth.
Fraser recovered from a disastrous double bogey on the second hole to card four birdies on his way to a one-under-par round of 70.
The day wasn't so good for defending champion Alexander Noren of Sweden.
Noren hit a 10-over-par 81 that included two birdies, six bogeys and one double-bogey.
He also shot a seven on the par-three third hole as he made a terrible start to his title defence.