Candidates from new Prime Minister Yukio Hatoyama's party were set to win Sunday in two by-elections for Japan's upper house, media said, in the first test for the centre-left government. Candidates for Hatoyama's Democratic Party of Japan (DPJ) faced those backed by the main opposition Liberal Democratic Party (LDP) in central Kanagawa and Shizuoka prefectures, with the official results to be announced later Sunday. Exit polls by public broadcaster NHK reported DPJ's Yoichi Kaneko is certain to win the seat in Kanagawa, while DPJ's Hirokazu Tsuchida is sure to beat his opponents in Shizuoka. The likely outcome provides an indication that the DPJ, which won a sweeping victory in the August lower house elections, may have a better chance to control the upper house after a nationwide poll for the chamber next summer. With 123 seats in the 242-member upper chamber, the DPJ and its coalition partners -- the People's New Party and the Social Democratic Party -- already have a majority, but Hatoyama's party alone held only 112 seats before Sunday. With two more seats likely to be added in the upper house, it will give momentum to Hatoyama, whose first parliamentary session starts Monday. The by-elections were also a test for LDP's new leader, Sadakazu Tanigaki, who is seeking to rebuild a once-powerful political party that ruled Japan for more than half a century. The LDP, led by former prime minister Taro Aso, suffered a historic blow at the hands of Hatoyama's DPJ in the August elections. 