Day posts best Riviera score in PGA event

Jason Day has credited a realisation not to "get angry" with Riviera Country Club for his lowest round at the Los Angeles course.

The former world No.1 had never broken 70 in 12 previous rounds at Riviera, but posted a three-under-par 68 on day one of Tiger Woods' Genesis Invitational.

Day sits four shots behind first round leader Matt Kuchar (64).

Day, a 12-time US PGA Tour winner, had never recorded a result better than a tie for 62nd in four starts at Riviera and had missed the cut twice.

But the 32-year-old said he lowered his expectations to set himself up for the rest of the week.

"I realised I can't come here and get angry, because it just won't help," Day told AAP.

"I knew I had to come into a week like this with a different mindset. I changed the way I view this course, because I actually really like it.

"I haven't had greatest finishes here, so I brought down my expectations to take the weight off my shoulders.

"It meant I could just go out there and play freely today."

Day said that was particularly difficult given the tournament had been rebranded this year as Tiger Woods' own US Tour event with invitational status and limited field of 120 golfers.

"Yes, it's a big week and there are a lot of good players here, so your expectations can go up pretty dramatically," he said.

Day's scrambling was remarkable on Thursday, made more difficult by the fact he hit just five of 14 fairways and 12 of 18 greens in regulation.

But he saved par five times from six attempts to keep himself well in contention.

"Overall, it was a solid day. If I missed the fairway I put myself in position to save par," Day said.

"I'm very pleased with the start and I'm putting better than I have in a while. Hopefully I can keep that up in the next three rounds."