Seguin's tally late in the first period put the Stars ahead 3-1 and his assist on Jamie Benn's goal midway through the second turned out to be the winning margin for Dallas, which was coming off a 2-1 shootout loss to Winnipeg Saturday.
Ruff, who was part of the Sabres organization for 26 years -- including 14 as its head coach -- was fired in February and hired to guide the Stars in June. He was given a standing ovation and a video tribute in his first visit to Buffalo since the move.
Mark Moulson, acquired from the New York Islanders in a trade for high-scoring Thomas Vanek Sunday, scored two goals in his debut for the Sabres, who fell to 2-11-1 on the season.
Notable deaths of 2014 [PHOTOS]