World number 1 Scottie Scheffler's joint-record streak of sub-70 scores end on Thursday
Scheffler is one of 10 players from the United States' team to participate in the Procore Championship at Napa this week
He has not finished lower than eighth at any event since March, said afterwards: "I think it was a pretty frustrating day overall.
Scottie Scheffler's Ryder Cup team-mates have no concerns over his form, despite the world number one seeing his joint-record streak of sub-70 scores end on Thursday.
Scheffler is one of 10 players from the United States' team to participate in the Procore Championship at Napa this week, as they gear up for a home tournament at Bethpage.
Russell Henley shot a first-round 65, putting him two shots behind the leader, Canadian Mackenzie Hughes. U.S. Open champion J.J. Spaun carded a 67, but none of the other eight USA players managed below 70.
That included Scheffler, who was forced to settle for a two-under-par round after a wild tee shot on the 18th hole.
Before this event, he had recorded 21 successive scores of 70 or under starting at the Travelers Championship in June, matching Patrick Cantlay for the longest such streak in the modern era.
Scheffler, who has not finished lower than eighth at any event since March, said afterwards: "I think it was a pretty frustrating day overall.
"I felt like I did some things well out there, I just wasn't quite getting the reward."
Spaun shrugged off Scheffler's disappointing day, saying: "This is his first go around here. It's very goofy.
"I don't think I liked this place the first couple of times I came here, but you learn how to play it, you learn where to miss.
"The greens, especially in the afternoon, are not great. He just barely missed a few putts. That would have kept his streak going. He'll be fine."
The Ryder Cup begins on September 26, with the USA looking to make it six successive home winners. Europe earned the last away win in the event, triumphing by a single point at Medinah in 2012.
