Casey, the 12th seed, beat Colin Montgomerie, 6 & 5. Micheel took a 2-up victory over Karlsson.
Casey and Montgomerie will be teammates next week at the Ryder Cup.
Casey and Micheel will play in a 36-hole final for the more than $1.86 million first-place prize -- largest in the world among officially sanctioned events. The loser will receive $745,760 for second place.
"I figure I am a little bit of an underdog again," Micheel said. "I don't know if there will be anybody out there rooting for me except my caddie and my wife."