Red Dead Redemption was comfortably the top selling game in the US during May, shifting 1.5 million copies compared to Mario Galaxy 2's 563,900, according to the NPD Group.
The Xbox 360 version of Rockstar's western claimed the majority of sales, a feat matched by the 360 edition of UFC 2010: Undisputed, which placed fourth on the monthly chart with 221,100 copies shifted.
Alan Wake debuted in eighth place, but sales figures for the game weren't revealed.
NPD analyst Anita Frazier said that in its first month Red Dead Redemption topped lifetime sales of its predecessor, Red Dead Revolver, which released in May 2004.
01. Red Dead Redemption (Take-Two, Xbox 360), 945,900
02. Red Dead Redemption (Take-Two, PS3), 567,100
03. Super Mario Galaxy 2 (Nintendo, Wii), 563,900
04. UFC 2010: Undisputed (THQ, Xbox 360), 221,100
05. UFC 2010: Undisputed (THQ, PS3), 192,300
06. Wii Fit Plus (Nintendo, Wii)
07. New Super Mario Bros. Wii (Nintendo, Wii)
08. Alan Wake (Microsoft, Xbox 360)
09. Pokemon SoulSilver Version (Nintendo, NDS)
10. Skate 3 (Electronic Arts, Xbox 360)