Shawn Green also homered and Javier Vazquez (4-2) earned his fourth victory in his last four starts, allowing two runs on seven hits with eight strikeouts in seven innings.
Glaus' home run -- the sixth-longest in the eight-year history of Bank One Ballpark -- was his ninth of the season, tying him with Chicago's Derrek Lee for the NL lead.
Oliver Perez (1-4) was the loser.
Pittsburgh's Matt Lawton hit a two-out homer in the ninth.
Nationals 9, Giants 3
In San Francisco, Ryan Church hit a three-run double, and Brad Wilkerson had three hits and drew a bases-loaded walk as Washington thrashed San Francisco.
Jon Rauch (1-1) pitched three effective innings for the win.
Deivi Cruz homered for the Giants, who lost their third straight following a six-game winning streak. Noah Lowry (1-3) was the loser.
Injured Mariners shortstop Pokey Reese, who has yet to play for Seattle this season, has undergone surgery on his sore right shoulder.
Also, catcher Dan Wilson is scheduled for surgery on May 20 to repair the anterior cruciate ligament in his right knee, which he tore on Wednesday during a loss to the Los Angeles Angels.
The procedure on Reese was performed on Thursday. The 31-year-old Reese, on the 60-day disabled list all season, will return to Seattle for rehabilitation.
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