Melbourne: Andy Murray breezed into the quarter-finals of the Australian Open on Monday after Mikhail Kukushkin retired due to injury in their third set.   

Murray, who had toiled against the Kazakh in the Brisbane warm-up tournament, was leading 6-1, 6-1, 1-0 when Kukushkin said he could not continue due to a hip flexor injury, allowing the Briton to retreat from the scorching heat on Rod Laver Arena.   

World number four Murray, the runner-up at Melbourne Park for the last two years, will next play Japan's Kei Nishikori, who stunned French sixth seed Jo-Wilfried Tsonga in five sets.   

"Just boring" was how Murray described his 49 minutes on court against the hobbled Kukushkin and said he would have to hit the practice courts to make sure he did not lose his rhythm.   

But while the Scot was aware he had not been given a proper workout he was pleased to keep his powder dry for the quarter-finals.   

"You can't look at it as a negative. At this stage of the tournament to be off the court in 45 minutes or so isn't bad," he told reporters. "It's perfect because you conserve energy."   

Murray said Kukushkin made the right decision to quit.   

"I thought it was best he retired because it was pointless. The people probably weren't enjoying the match that much. I certainly wasn't because nothing was happening.   

"Sometimes it's best just to stop."   

The 24-year-old credited new coach Ivan Lendl with instilling a little bit of extra confidence in him and said he was soaking up the eight-times grand slam champion's knowledge.   

"I think because it's him you're kind of like a sponge," he added. "You're kind of absorbing a lot of different information. You're asking a lot of questions and you're getting a lot of good answers, interesting ones.    

"When you just get that little bit of extra help from someone that's been there and done it many, many times, it helps."