HAIKOU, Feb. 8 (Xinhua) -- Top-ranked Wang Chuqin of China beat Japan's Tomokazu Harimoto 4-2 in the men's singles final to defend his title at the Asian Cup table tennis tournament here on Sunday.   Harimoto started strongly with aggressive returns to lead 2-1 after three games (11-9, 8-11, 11-7), before Wang bounced back to rally past with three consecutive wins 11-5, 11-8, 11-6 to lift the trophy at home.   Earlier in the day, Japan's Shunsuke Togami cruised past Chinese Taipei's Chang Yu-An 4-1 to finish third in the men's singles.