Democrats retained their overwhelming majority in the Massachusetts state Senate, leading in most contested races including the hard-fought battle for the seat held by Senate President Therese Murray, who fended off a challenge brought by the Republican who nearly beat her two years ago.

“This is a big red district and I’m the only Democrat ever elected here,” said Murray, who defeated her opponent, Thomas F. Keyes, by a wide margin. Two years ago, Keyes won nearly half of the vote. “Republicans and unenrolleds came out and voted for me. It makes me feel that people appreciate the job I’m doing and I appreciate their vote.”