Assistant Scott Brooks was appointed interim coach.
The firing came after the team's 10th consecutive loss, a 105-80 defeat Friday night to New Orleans. The Hornets played for two seasons in Oklahoma City.
The Thunder relocated from Seattle in the offseason after a franchise-worst 20-win season to start Carlesimo's run. Carlesimo was 21-74 in just more than one season with the franchise.
Oklahoma City played the Hornets again Saturday night in New Orleans.
The Thunder also let go assistant coach Paul Westhead , who led the Phoenix Mercury to the 2007 WNBA title after a successful run in college.
HEAT: Guard Dwyane Wade missed Miami's shootaround practice Saturday morning with an unspecified illness. The team said he was expected to play Saturday night, when Miami played host to Indiana.
Wade is the NBA's second-leading scorer at more than 28 points per game, trailing only Cleveland's LeBron James .
RAPTORS: Forward Jermaine O'Neal did not practice Saturday and was listed as day-to-day after straining his surgically repaired left knee against New Jersey on Friday night.