Kevin Frandsen stepped into the batter’s box for his first and only at-bat with one out and one objective: Score the man on third. A home run, a sac fly, it didn’t matter. “Pinch-hitting is an unselfish at-bat. It’s a team at-bat,” he said. “I’m not praying for that ball to get down. I mean, it’s great. But I’m hoping just to get that run across, because if I go up there and don’t get that run across, I didn’t do my job.” Frandsen lifted a pinch hit double to center field, scoring pinch runner John McDonald from third for the go-ahead run and chasing Jordan Zimmermann from the mound in the seventh inning as the Phillies used a bit of small ball to slip past the Washington Nationals, 3-1, and take three of four games in the series Thursday night at Citizens Bank Park. Philadelphia has won three consecutive series against Pittsburgh, Atlanta and Washington — three of the top teams in the National League — and is within 7 ½ games of the NL East lead with three games remaining before the All-Star break. The Phils open a three-game set today against the Chicago White Sox, one of the American League’s doormats. “We’ve got to play hard. We’ve got to outplay them. We’ve got to do the same thing against the Chicago White Sox that we did against Washington and against the Atlanta Braves,” Phillies manager Charlie Manuel said. “We’ve got to play harder and harder and not let up.” McDonald was running for Darin Ruf, who opened the seventh inning with a double to left, and advanced to third on a sacrifice bunt by Carlos Ruiz. The Phils solidified the victory by manufacturing an insurance run in the eighth inning, when Chase Utley doubled to center, advanced to third on a fly to right by Domonic Brown and scored when Michael Young hit into a fielder’s choice, sliding across the plate to beat the throw from second.