In a boost to the ruling Congress in Karnataka, the party on Saturday swept the by-polls to three Assembly segments, causing a major setback to the BJP-JD(S) alliance in the state. The Congress has retained Sandur, the seat considered to be its strong hold, and has also bagged Shiggaon and Channapatna segments, which were earlier held by BJP and JD(S) respectively. The November 13 by-polls to Sandur, Shiggaon and Channapatna Assembly segments had witnessed a fierce fight between the ruling Congress and a combative BJP-JD(S) alliance. The by-polls to Sandur, Shiggaon and Channapatna were necessitated as the seats fell vacant following the election of their respective representatives -- E Tukaram of Congress, former CM Basavaraj Bommai of BJP, and Union Minister Kumaraswamy of JD(S) to Lok Sabha in May elections. The by-polls witnessed a straight fight between the ruling Congress and BJP in Sandur and Shiggaon segments, while in Channapatna, JD(S) which is part of the NDA alliance to