SYDNEY - Former U.S. Open champion Juan Martin Del Potro underlined his status as a dark horse for next week’s Australian Open by hammering Dmitry Tursunov to reach the final of the Sydney International on Friday.The lanky Argentine, who will be seeded fifth in Melbourne, hit nine aces as he brushed aside the Russian fourth seed 6-4 6-2 in just over an hour to reach his seventh final in the last 12 months.Two of those finals were at Masters events in Shanghai and Indian Wells, an indication for some that Del Potro might be returning to the level of form that he reached to win the 2009 U.S. Open title before a wrist injury nearly ended his career.The 25-year-old will meet Australian defending champion Bernard Tomic or Ukrainian qualifier Sergiy Stakhovsky in Saturday’s final at Sydney’s Olympic Park.Del Potro was seeded to meet world number one Rafa Nadal in the quarter-finals of the year’s first grand slam, while Tomic was revealed as the Spanish 13-times grand slam champion’s opponent in the opening round in Friday’s draw.World number five Del Potro and Australian veteran Lleyton Hewitt are the only grand slam winners apart from Nadal, Roger Federer, Novak Djokovic and Andy Murray still active in men’s tennis and the Argentine believes he might soon be challenging the leading four players again in major finals."I think I’m getting closer to the top four guys,” he said on court at the end of his match. "They are still playing such great tennis but if I am fit, I will try to be dangerous for them.”