Left-hander Mitchell Parker threw seven shutout innings, and Luis Garcia Jr. had three singles and two RBIs and the Washington Nationals beat the Houston Astros 6-0 on Sunday. The Nationals have won three of their past four series after starting the season 2-6. After allowing two runs over five innings last Monday in his major league debut, a 6-4 win over the L.A. Dodgers, Parker (2-0) was even more effective in his second major league start, allowing three hits, striking out eight and walking none, throwing 57 of his 73 pitches for strikes.