Japan's Ryosuke Irie outpaced American Matt Grevers to win the 100-meter backstroke on the first day of competition at the Pan Pacific Championships on Thursday.

There was also a gold medal for Daiya Seto in the men's 200 butterfly, but Ryosuke Hagino had to make do with the silver in the men's 200 freestyle.

Irie, the London Olympic bronze medalist, posted a time of 53.02 seconds at the Gold Coast Aquatic Centre to beat out Grevers, who took silver in 53.09. Ryan Murphy of the United States took the bronze medal with a time of 53.19.

"I am really happy that I was able to win but can't be satisfied with this time and have to aim higher," said Irie, who also won silver in the 200 at the London Olympics.

"I won't be able to compete on a world level with a time like this and want to be a swimmer that can post a good time whatever environment I am in."

Japan's former world gold medalist Junya Koga was sixth in 54.02.

In the 200 fly, Seto saw off the challenge of Brazil's Leonardo De Deus, touching the wall in 1 minute, 54.92 seconds. De Deus timed 1:55.28 and American Tyler Clary was third in 1:55.42. Masato Sakai followed in fourth in 1:56.64.

Hagino came up short in his bid for gold in the first men's final of the night, timing 1:46.08 to finish runner-up to Thomas Fraser-Holmes of Australia (1:45.98). Cameron McEvoy of Australia placed third in 1:46.36.

Elsewhere for Japan, Natsumi Hoshi (2:06.68) took the silver medal in the women's 200 butterfly. American Cammile Adams claimed the gold in 2:06.61.