APPRENTICE Simon H. K. Yim has laboured long and hard to try and carve out a niche for himself in Hong Kong's bustling racing set-up and tonight at Sha Tin he moves to centre stage for the first time in his relatively short career. Yim's career looked to be virtually over before it started when two years with French trainer Patrick Biancone produced a lot of race rides, no winners and too much adverse comment to be considered useful to his prospects. With the invaluable help of his master, however, Yim persevered and has succeeded to the extent that his engagement for any horse does not now invoke a reaction of looking elsewhere. He has proved his worth on several occasions this season and produced a personal best last month when notching a Sha Tin double. One of those winners was Special Warning and this striking individual is the reason why Simon, affectionately known as ''Hong Kong'' Yim, is in the spotlight. Trained by Derek Cruz and responsible for an excellent win under Yim, Special Warning goes for the featured Sha Tin Vase over 1,600 metres - and the sparks should fly. It is a measure of the owner's faith in young Yim that the apprentice is retained on the horse as no claims are permitted in this special conditions event. But Yim's continued engagement was never in doubt as he explained: ''The owner has been my good friend for some time and he was hoping that he would get a really good horse. ''I was very thrilled by his win last time and it was not a big surprise to me although the public did not like the horse's chances. He had run well at his first start and Derek Cruz was sure he had improved and he felt as if he had. ''It was a good win and we are all hoping that he can prove to be a top horse in the future,'' said Yim. Special Warning is the only progeny of Warning so far racing in Hong Kong and his sire is enjoying near celebrity status in the UK where he was leading first season sire last year. A top racehorse himself, Warning annexed over HK$6 million in stakemoney winning the Group One Queen Elizabeth II Stakes, the Sussex Stakes and the Queen Anne Stakes. He had a three-year-old Timeform rating of 136. Trainer Cruz has landed a potential top-liner in Special Warning judging by his win last time out and there was certainly nothing wrong with the horse's work at Sha Tin on the grass track on Tuesday. He has clearly come out of his last race particularly well and he must be considered a top chance in what does not look a really competitive Sha Tin Vase. Without any doubt Sumotori, from the Ivan Allan stable, will be the choice of most punters to beat home Special Warning and, on the book, there is virtually no contest. In Special Warning's race last time, Sumotori finished third and was only three-parts of a length from the winner. On that occasion Sumotori was giving Special Warning 16 pounds with Yim's claim while tonight he must give him only two pounds. One stone in weight for just three quarters of a length suggests that Sumotori has it all over Special Warning - but, of course, it doesn't always work out despite, on this occasion, the quite staggering figures. There can be no real doubt that Special Warning has come on from that last race and he is, in the opinion of some judges, a more than decent horse who could go higher than this. The blinkers go on Sumotori for the first time and he cannot be really seen as a potential champion. He's a handy horse and dangerous where he's placed now. The decision taken before his previous race to step him up in distance was a wise one and almost came off - were it not basically for Special Warning. There are very serious question marks over a number of these runners - not least the top two and those at the bottom of the scale. Sure Win King has not proved to be effective to date over 1,600 metres and Auto-Matching is tackling it for the first time. Auto-Matching is a good type of horse and came through from behind last time before being caught very close home over 1,400 metres by Easy Fit. He had previously won as he pleased over the longer Sha Tin sprint and it may be that - at this stage - up to 1,400 metres might be his forte. Magic Joy and Medic Star have both failed over similar trips in the past and Turf King, although not a bad type, gave no encouragement to those who supported him on his debut when ridden by Basil Marcus. The trip should not be a problem for the son of Nishapour but he would probably benefit from being held up and those tactics might be adopted by RAmbo Tse Wai-ho tonight. Hong Kong Supreme should be included in quinella and tierce bets as he does have form over 1,600 metres and looks ready to run his best race to date. He has in-form Eric Legrix aboard and they can go close. Jade, to be ridden by Damien Oliver, has placed form at the trip and could have admirers while Starbuck would seem to have it all to do. He did run second in the Happy Valley Vase, beaten by Stellar Express. He has plenty still to learn about the game and Starbuck, winner to date of a Class Five race, is tackling tough company here. If he does run a place it is going to make a complete mess of his current handicap mark as he is a Class Four horse tackling a race that includes one Class One horse. Clearly owners who enjoy the sport rather than a bet. For those of us who do relish a tilt against the tote, Special Warning does make appeal but Sumotori must be in there together with Hong Kong Supreme. And it could be worth taking a chance with Turf King for added value as he must be at big odds and has a squeak.