Casey’s four-under-par round leaves him in a tie for eighth, four shots off the early pace set by Austria’s Sepp Straka after a first day which was interrupted for more two hours because of lightning in the area.
Casey and British teammate Tommy Fleetwood, who is one-under, are staying in the Olympic village and the 44-year-old said the performances of the likes of Adam Peaty, Tom Daley and Tom Dean had given him extra motivation to try and match Justin Rose’s gold medal-winning display of five years ago.
“There are other sports which are the traditional, as we would say, Olympic sports we are used to watching and we are not under the spotlight so to speak,” Casey said. “But I feel there is an immense sense of responsibility. I’ve got to try and deliver as much as I can.
“You feel that with the other athletes because everyone else is performing so brilliantly, I want to perform and live up to their expectations as well.”
Thailand’s Jazz Janewattananond is the closest challenger to Straka on seven-under, with Belgium’s Thomas Pieters and Mexico’s Carlos Ortiz a further shot back.
Xander Schauffele and Patrick Reed are the best of an American quartet that also features Open champion Colin Morikawa, on three-under, while local hero, Masters winner Hideki Matsuyama is two-under, the same score as Rory McIlroy, who is competing for Ireland at these Games.
“When Hideki won the Masters, the first thing I thought of was how good is the atmosphere going to be at the Olympics, but unfortunately that’s not the case,” McIlroy said of the absence of fans on course.
“That’s the unfortunate part about it but there’s three medals up for grabs and we’re all here trying to play for them.”