<Li> Carrie Preston as Mandy Newhouse, twin sister of Samantha and one of Kimmy's bridesmaids . </Li> <Li> Susan Sullivan as Isabelle Wallace, wife of Walter, mother of Kimmy, and future mother - in - law of Michael . </Li> <Li> Christopher Masterson as Scotty O'Neal, youngest son of Joe and younger brother of Michael and future brother - in - law of Kimmy . He serves as his brother's best man at his wedding . </Li> <Li> Paul Giamatti as a bellman who encounters Julianne in a hotel hallway . </Li>

Who plays the best man in my best friend's wedding