Andy Murray may have reaching the semi-finals of the Brisbane International yesterday but the US Open champion has fallen short in a pledge to curb his habit of swearing on court and has toned down the pledge itself, writes Will Swanton.

He said last month that he wanted to clean up his act after repeated warnings for unsavoury language, but audible obscenities were uttered in both his first two matches in Brisbane, against Australia's John Millman and Uzbekistan's Denis Istomin.

Spectators at Pat Rafter Arena clearly heard Murray barking the occasional swear word, something the world No.3 has done throughout his career to let off steam when dissatisfied with his performance. He beat Istomin 6-4, 7-6 (7-3) to book a semi-final place – it was scheduled for the early hours of this morning – against Japan's Kei Nishikori, who defeated Alexandr Dolgopolov (Ukraine) by the same score.

"Obviously, me saying 's***' or whatever is bad and wrong, and it's something I want to try to stop doing," Murray was quoted as saying last month, but he declined to make the same promise ahead of his match with Nishikori. "I don't really know how that will go," he said. "I get asked a lot about it after matches. It can be picked up on the microphone or whatever. No-one has mentioned it [in Brisbane] but the microphones at the Aussie Open are all around the court, so we'll see."

Murray denied his attempt to tone down his language was because he felt more of a role model after winning the Olympics and US Open last year. He claimed worse levels of swearing from other players went undetected because it was not delivered in English. "Where it [the pledge to stop swearing] came from was when I was asked a question," he said. "I was doing an interview over the phone. I was asked about swearing on the court. I said 'obviously I don't mean to do it. I don't want to do it.' I didn't make promises or guarantees. Then it came out that I've said I will stop swearing. What I also said was that a lot of players swear on court and a lot of people say a lot worse things than me, in other languages. It doesn't get picked up the same. So while I'd love to stop doing it, I try not to [do it]. But I can't guarantee it."