NAGOYA, Japan, — South Korea trounced Vietnam 46-18 for its fifth consecutive victory in women's handball at the Aichi-Nagoya Asian Games on Saturday, setting up a final showdown against the defending champion Japan with the gold medal at stake. Jo Eun-been led the balanced attack with eight goals at Entrio in Inazawa, just northwest of Nagoya, while Lee Hye-won and Cha Seo-yeon contributed seven goals each. The outcome was hardly in doubt, as South Korea built a 7-2 lead in the first 10 minutes and held Vietnam to just two goals in the final nine minutes of the first half. South Korea led 33-15 midway through the second half and finished the contest on a 13-3 run. The women's handball competition here does not feature a knockout stage. Instead, all seven teams will play each other once and medals will be awarded based on their final round-robin standings. Through Saturday, South Korea and Japan are the only undefeated nations, with five wins apiece, and the winner of their matchup Sunday will take the gold medal. Women's handball was added to the Asian Games in 1990, and South Korea won