Marc shot out of the block and beat his brother Alex, the pole-sitter, into the opening turn. Alex was able to quickly regain the lead but ran wide a turn later to hand it back, and Marc did not make any mistakes from that point on.
Victory moved seven-times MotoGP champion Marquez up to 399 points in the championship standings, 44 ahead of Martin, who did not compete after fracturing his wrist.
Saturday's sprint winner Pedro Acosta of KTM finished second, while Gresini's Alex was third.