On a night when every Pirates starter had at least one base hit, Bay stood out with a two-run home run, a double and four RBIs.
After a loss Wednesday, Bay slugged the Pirates to another road victory when he went 3-for-4, scored three runs and stole two bases in Thursday's series finale.
Bay also stole two bases that night, his 12th and 13th of the season.
"I thought he could [steal] 20 this year and eventually be a 30 [steals]/ 30 [home runs] guy," Pirates manager Lloyd McClendon said Sunday.
The Canadian-born outfielder added another stolen base Sunday. Dating back to last season, he has a current string of 15 consecutive stolen bases without getting caught.
"Batting in the three-hole and being a little bigger than [the average] basestealer, I get forgot about a lot of times," Bay said. "Over the course of a season, if I can steal 30 bags here or there, I think that would go a long way."
Another thing that has been going a long way all season has been Bay's hits: The 2005 All-Star's 23 home runs are just three shy of the total he reached last season. Additionally, he ranks among the league leaders in RBIs (69), hits (134), slugging percentage (.564) and batting average (.305).
With a first-inning single against the Astros on Sunday, Bay extended his streak of reaching base to 29 consecutive games. He added a home run in the fourth inning
Other nominees this past week included New York's David Wright (.440, 1 HR, 9 RBIs); Jose Guillen (.412, 2 HR, 7 RBIs), John Patterson (2-0, 2.63 ERA, 7 SO) and Jose Vidro (.478, 1 HR, 3 RBIs) of the Nationals; Houston's Morgan Ensberg (.368, 3 HR, 6 RBIs); Dioner Navarro (.412, 1 HR, 2 RBIs) and Brad Penny (1-0, 1.13 ERA, 13 SO) of the Dodgers; Florida's A.J. Burnett (2-0, 0.56 ERA, 10 SO) and Josh Beckett (1-0, 1.80 ERA, 10 SO); Sean Casey (.476, 2 2B, 1 RBI), Ken Griffey Jr. (.286, 3 HR, 8 RBIs) and Jason LaRue (.375, 1 HR, 4 RBIs) of the Reds; Philadelphia's Pat Burrell (.364, 2 HR, 10 RBIs) and Ryan Howard (.391, 2 HR, 9 RBIs); Chris Carpenter (1-0, 2.00 ERA, 8 SO), Mark Grudzielanek (.360, 1 HR, 7 RBI) and So Taguchi (.435, 4 RBIs, 3 SB) of the Cardinals; Chicago's Michael Barrett (.412, 2 HR, 2 RBIs) and Todd Walker (.417, 1 2B, 1 RBI); Todd Helton (.400, 1 HR, 3 RBIs) of the Rockies; Arizona's Shawn Green (.450, 2 HR, 4 RBIs); and Bay's teammates Jose Castillo (.409, 2 HR, 6 RBIs), Jack Wilson (.360, 2 HR, 8 RBIs) and Dave Williams (2-0, 0.60 ERA, 7 SO).
As part of the award, Bank of America will donate $1,000 on behalf of Bay to the Little League Urban Initiative.