SEATTLE (AP) — Christian McCaffrey rushed for 114 yards and two touchdowns in the first half, and the San Francisco 49ers built a 21-point lead by halftime, rolling to a 31-13 win over the Seattle Seahawks. The 49ers won their fourth straight against their division rivals and have a two-game lead over Seattle in the NFC West. San Francisco won its third straight following a three-game losing streak and picked up its 10th straight win against an NFC West opponent. McCaffrey was terrific, running through arm tackles and breaking off a handful of big plays. McCaffrey rushed for touchdowns of 8 and 1 yards as the 49ers built a 24-3 halftime advantage.