Swim great Ian Thorpe disappointingly finished 15th overall in the Beijing short-course World Cup 100m freestyle heats Tuesday as he tested his favoured stroke for the first time in five years. The 29-year-old Australian, who finished well out of the medals in his comeback from retirement at last weekend\'s World Cup event in Singapore, timed 50.21sec, 0.61 off the qualifying pace. The five-time Olympic champion also missed the final of the 100m individual medley by two-hundredths of a second, as hopes of a quick return to form faded. He will also swim the 100m butterfly on Wednesday. Thorpe will also compete in Tokyo this weekend as he builds towards Australia\'s Olympic trials in March, where he will bid to set up a London 2012 match-up with American superstar Michael Phelps. \"I think a lot of people underestimated the complexity of swimming,\" Thorpe said in Singapore, where he finished second-last in the 100m individual medley final and crashed out in the 100m butterfly heats. \"I told people if I was to start swimming again it would take me three years to get back to where I was. I\'m planning on it not taking that long. I\'m trying to fast-track that now.\" He added: \"If I get to the end of Tokyo and I\'m not swimming faster I am going to be very frustrated and I\'ll be quite annoyed, because I expect this of myself at the moment.\" Thorpe announced his comeback in February and has been training in Switzerland under renowned coach Gennadi Touretski. He collected five Olympic gold medals in 2000 and 2004 along with 11 world titles before quitting in 2006 aged just 24, citing a lack of motivation.