DENMARK'S Kenneth Carlsen showed Hongkong tennis fans why he is one of the hottest properties on the world circuit by beating fifth-seeded American Brad Gilbert 6-4, 6-4 in the Salem Open second round at Victoria Park yesterday. Carlsen, who hopes to celebrate his 20th birthday tomorrow with a semi-final appearance, climbed a staggering 967 places in the rankings during 1992 to end the year at number 69. And now he is up to 53 - and sure to rise further as he continues to improve his game. What is all the more remarkable about his success story is that tennis was his third sport, after soccer and swimming. The Copenhagen-born left-hander explained: ''Like every boy in Denmark, soccer was my first sport and I started playing at 41/2-years-old and played until I was 12. ''I took up swimming from the age of five to 10 and it was only through my father that I began to play tennis. ''He started playing tennis three or or four years before me and I used to go along with him when I was eight years old and play long into the evening. ''I wanted to join the club when I was eight but he said I was too young and had to wait until I was 10 - but then he thought it would be a good idea for me to start at nine.'' With a natural talent for the game, Carlsen improved rapidly on clay courts from the age of 10 by working with Swedish coaches, including Martin Bohm, whose students have also included world-ranked Swedish players Nicklas Kulti and Magnus Larsson. ''Through them I learned to appreciate that talent and hard work must go together and I got inspired by them to play junior tournaments. ''At that time, Borg, Connors and McEnroe were on top and you'd want to be like them.'' Just over 12 months ago, as Carlsen set out on the long road to the top of the rankings, he was having to qualify for minor satellite tournaments in Germany. His big break came with a wild card entry into an ATP Tour stop in his hometown of Copenhagen, where he beat top seed Alexander Volkov to reach the quarter-finals. ''That gave me a lot of confidence and belief that I could do well if I continued to improve. But I am surprised how quickly I went up the rankings. ''I do not want to set myself a target for this year, though, because it's more important to concentrate on improving my game. If I do that the results will take care of themselves.'' Carlsen said there were around 125,000 tennis players in Denmark's population of five million but the sport remained fourth in popularity behind soccer, badminton and handball. ''The next Danish player after me in the rankings is about 270 but hopefully we'll get a few more players up to the top. I hope I can be an inspiration but only time will tell.'' Gilbert, who was beaten by Pete Sampras in last week's Japan Open final in Tokyo, lost his second service game in the first set yesterday and Carlsen stayed in front to hold on 6-4. Carlsen looked to have the match wrapped up when he served for the match at 5-2 in the second set but inconsistency crept into his game under a fierce sun and Gilbert closed the gap to 5-4. Carlsen produced one last effort, though, and won the tie on his second match point when an out-of-sorts Gilbert overhit a forehand return.