Mac Williamson smacked a two-run home run in the sixth inning and Chris Stratton pitched four-hit ball into the seventh Monday night, helping the San Francisco Giants turn back the Washington Nationals 4-2 in the opener of a three-game series in San Francisco. Williamson, promoted from the minors last week when Hunter Pence was placed on the disabled list, drove in three runs, two with his second homer in his first 13 at-bats in the majors this season. The win in the opener of a 10-game homestand was the Giants' third in their last four games.