Australian Open: Andy Murray through to quarter-finals after weary Kukushkin retires Published on Monday 23 January 2012 08:46 Andy Murray took just 49 minutes to progress to the quarter-finals of the Australian Open today after Kazakhstan's Mikhail Kukushkin was forced to retire through injury after losing the opening two sets. Kukushkin beat Gael Monfils in five gruelling sets in the previous round and those exertions seemed to hinder him from the start, with Murray leading 6-1 6-1 1-0 before Kukushkin pulled out with a left hip flexor problem. The contest was one-sided from the outset, making it difficult to gauge the quality of Murray's performance, but the world number four will be delighted to have got through with the minimum of effort, conserving energy on a hot Melbourne day. Kukushkin looked nervous early on and three unforced errors in the first game handed Murray a break. And although Murray was also a long way from his best in the opening stages, he broke again for a 3-0 lead. Kukushkin finally displayed a bit of fight to hit back for 3-1, only to relinquish his serve once more after pushing two backhands wide. The world number 92 gave an indication he was perhaps not 100% physically when he called for the trainer at the next change of ends, but Murray was in no mood to loosen his grip on proceedings and another break won him the set. Murray remained in complete control at the start of the second set, breaking again for a 2-0 lead after stepping in to crush a second serve to Kukushkin's feet. But, as he did in the first, he failed to back up the break as a poor set of points, culminating in a backhand which hit the net halfway up, gifted his opponent a break back. Kukushkin was still struggling on serve, though, while his physical state appeared to be getting worse. In a bid to keep the points short he started rushing the net, but that just played into the Scot's hands as he broke once more and then held with ease to go 4-1 ahead. Murray was finally starting to find his game and some clean hitting saw him go 5-1 up before he held to love to claim the second set 6-1, again in 22 minutes. From that point there was little prospect of a Kukushkin victory and, having lost his serve for an eighth successive time, he offered his hand as Murray moved through to the quarter-finals. "I played him a few weeks ago (in Brisbane) and it was a tough match," Murray said. I expected another one today but it's so hot. I get to conserve a bit of energy but he was obviously struggling. When I saw him struggling I was just trying to get a few serves in and get him running. Murray's opponent in the next round will be Kei Nishikori, who stunned sixth seed Jo-Wilfried Tsonga to become the first Japanese player to reach the last eight of the Australian Open in 80 years. Nishikori, 22, outlasted Tsonga over three and a half hours to win 2-6 6-2 6-1 3-6 6-3 and advance to his maiden grand slam quarter-final.