Casey feeding off electric Olympic experience

Paul Casey has stood on the first tee at the Ryder Cup, heart beating out of his chest.

But he says his opening shot at the Olympics gave him chills on a whole new level.

Casey shot a solid four under par to sit four shots back from early leader, Austria's Sepp Straka, a solid foundation to build a challenge at the Kasumigaseki Country Club, as he and Tommy Fleetwood look to follow the lead of Team GB's Rio gold medallist Justin Rose.

"I just felt really proud, it was probably the coolest thing I've ever done in golf," he said.

"There was not an ounce of nerves, just 100 percent excitement. I've thought about this for so long because you can't count yourself as an Olympian until you've started your competition. It was brilliant but then I got down to business.

"There was a tension out there that is not normal, which was really cool. First round of a major there's a buzz but a jovialness, there was none of that, it was total business.

"This just feels very different, everyone here is all in and very aware of what that gold medal means. This might be the only chance I get to win an Olympic gold, I'll have other chances at majors."

Casey is embracing Olympic village life, doing his own washing and making his own lunches - his medal campaign is powered by ham sandwiches.

Normally superstitious not to touch a trophy he's not won - Casey made an exception for Matty Lee's gold medal.

But the 44-year old admits being around so many athletes in the peak of physical condition has given him a complex.

"I figured I'd never win a medal in synchronised diving," he joked.

"I'm in awe of what these sports do, the ability, talent and athleticism is everywhere.

Casey completed his round before heavy rain and thunder sent players scampering for shelter, Fleetwood was two under through 13 when play was delayed.

"We've got bicycles in the village and I'm barely keeping up with these four Aussie lads.

"I usually go for run at tournaments, but I've left my shoes at home, these guys are running at the same pace as me on the bike.

"This has been an inspiring week, I want to work out more, work harder on the golf course. Seeing the passion that people have for their sports is just really humbling."

Casey was arguably the pick of the big name players out early, with an unfamiliar look to the leaderboard.

Early frontrunner Straka was two shots ahead of Mexico's Carlos Ortiz and Belgian Ryder Cup star Thomas Pieters.

Masters champion and home hope Hideki Matsuyama finished six shots back from the leader after spurning a flurry of back nine birdie chances.

"It's a solid start and I did everything nicely," added Casey. "I don't what the winning score will be, probably 15 or 16 under - it depends on these weather conditions.

"I just need to eliminate the mistakes and what I didn't want to do was shoot myself in the foot. I'm happy with how I played, it was a clean card even if I didn't hit the ball brilliantly."