PHOENIX - The Phoenix Suns were supposed to be a young team on the rise in the NBA. They have fallen far short of expectations 21 games into the season, and that cost coach Frank Johnson his job.

The Suns fired Johnson on Wednesday and promoted his lead assistant Mike D'Antoni to replace him. D'Antoni makes his debut as Suns' head coach Thursday night when his team faces the New Orleans Hornets.

His instructions to his players: run, run and then run some more.

''We are going to try to be exciting,'' D'Antoni said. ''We are going to try to put up a lot of points. We have the talent, physical capabilities, a nice style of basketball that's fun for the players.''

Johnson had been with the Suns for a decade, first as a player who gained the nickname ''Fourth Quarter Frank,'' then as a community relations official and for five seasons an assistant coach.

''We have three of the best young players in the NBA on one roster,'' Suns owner Jerry Colangelo said. ''We've underachieved. We lost something coming in. Everybody's got to be in the trench together. It just didn't seem that way. Quite honestly, that's not pointing fingers at anyone. The bottom line was something had to change.''

The Suns have lost six of seven to fall 8-13 for the season.

''The more I saw on the floor, the more I disliked what I saw as it related to body language, communication or lack of same,'' Colangelo said.

D'Antoni, under contract through next season, said he'd try to get the running game in gear immediately and offered a semi-serious warning.

''It should be exciting the first couple of nights. Balls should be flying around. We'll try not to hurt anybody,'' he said.

Bryan Colangelo, the owner's son and president of the Suns' basketball operations, accompanied the team on its four-game trip to the East. He watched Phoenix blow a 22-point early lead in Orlando on Monday night and lose to a Magic team that had dropped 19 straight.

Injuries to Stoudemire and first-round draft pick Zarko Cabarkapa have added to the team's woes. Stoudemire is out for about four more weeks with an ankle injury. Cabarkapa will be sidelined for five to seven weeks with a broken wrist.

D'Antoni, 52, has dual citizenship in Italy and the United States. A star point guard at Marshall, he played one season for the Kansas City-Omaha Kings before spending 13 seasons with Milan of the Italian League.

He led the team to five Italian League titles and two Cups of Europe championships. D'Antoni coached Benetton Treviso of the Italian League from 1994-97, capturing the Cup of Europe title in 1995 and the Italian League crown in 1997. He returned to coach Benetton again in 2001.

D'Antoni was coach of the Denver Nuggets during the lockout-shortened 1998-99 season, and the team went 14-36. He returned to Benetton and coached the team to another Italian League title the following year.

''We've got to get some excitement into the arena,'' he said. ''Sometimes this year, it felt kind of down, like we were waiting to let the cannon fall on our head, like 'When are we going to mess up so people can talk bad about us?''