Sidney, playing just his second collegiate game after sitting through two suspensions, came off the bench and shot 7 of 12 in 19 minutes. He also made all five of his free throw attempts and grabbed six rebounds.
Kodi Augustus added 13 points and 11 rebounds for the Bulldogs (8-4), who snapped a two-game losing streak.
Mississippi State shot 42 percent in the first half to take a 37-24 lead at intermission. The Bulldogs held San Diego (2-10) to 30 percent shooting and without a double-digit scorer.
Mississippi State led by as many as 22 points with 5:27 left after an Augustus basket made the score 62-40.