'Responsible' Murray blows away cobwebs in Tokyo

Defending champion Andy Murray blew away the cobwebs with a 7-6 6-4 win over Croatian Ivo Karlovic in his first tennis match since winning last month's US Open.

The Olympic gold medallist said winning his first grand-slam title in New York had forced him to change his objectives and become more "responsible."

"I was so, I don't want to say 'obsessed' with winning a grand slam, but it was so important to me," world number three Murray told reporters.

"Sometimes during the year in certain matches I haven't done myself justice. I felt after the U.S. Open (I needed to) reset some goals.

"I was always focusing on the next grand slam rather than every tournament and every match I played.

"Now I feel like I can hopefully concentrate better, take more responsibility for my performances in every tournament throughout the year."

The Scot said he felt no different having finally won his first grand slam after losing in four finals.

"It didn't feel a whole lot different (stepping on court as a grand slam winner)," said the 25-year-old.

"Hopefully with time that will come," added Murray, who reached his first Wimbledon final this year before exacting his revenge on Roger Federer in the Olympic final in London.

"I think where I will feel it more will be if I'm getting to the latter stages of grand slams. Hopefully I will start feeling more confidence to go on to win."

Murray had been scheduled to open his Japan Open defence against Gael Monfils but the Frenchman pulled out with a knee injury, to be replaced by lucky loser Karlovic.