Another man in the vehicle — 23-year-old Duane Johnson, of Reno, Nev. — also was killed in the accident. He was believed to be a friend of Darr.
Darr, 25, was San Diego's opening-day center fielder in 2001, his first full big league season, and started 69 games.
Ben Howard, a 23-year-old pitcher who played for San Diego's Class-A and Double-A affiliates last season, was treated at the scene and released, Arizona Department of Public Safety spokesman Frank Valenzuela said. The team said he sustained scrapes and bruises.
"This is a very, very difficult thing to begin spring training with,'' Padres manager Bruce Bochy said. "It's such a tragic loss.''
Bochy said Darr "was a fun-loving guy who played the game like it was supposed to be played. He played all-out and that's going to be missed.''
Padres closer Trevor Hoffman broke down and cried when talking about Darr.
"We've lost a special teammate, a special person,'' Hoffman said. "There are a lot of heavy hearts in the locker room. There's a lot of shock in the clubhouse right now. ... You don't want to believe it.
"Michael was a free spirit. He was a happy-go-lucky guy. He embraced life. He embraced everybody in a special way. He always had a smile that lit up the clubhouse.''
Last year, Darr made 24 starts in center field and 45 in right, where Tony Gwynn hardly played because of leg injuries. Darr moved into the starting lineup after Ruben Rivera was released in spring training but eventually gave way to Mark Kotsay, who was obtained from Florida just before opening day.
Darr was good defensively but didn't have much power, hitting just two homers last year. However, both were game-winners in the Padres' last at-bat. He batted .277 with 34 RBIs.
Darr was the Padres' minor league player of the year in 1997 after being obtained from Detroit with another player for second baseman Jody Reed late in spring training.
In 2000, Darr shared the Padres' minor league player of the year award with Jeremy Owens. Darr hit .344 with 9 homers and 65 RBIs in 91 games with Triple-A Las Vegas.
He was recalled to the Padres on July 31. In his first game following the recall he hit the second pitch he saw for a two-run homer against Philadelphia. Darr also played in five games for San Diego in mid-April 2000 before returning to Triple-A.
The crash occurred about 2 a.m. Today was the voluntary reporting date for pitchers and catchers.
Darr became the second player in the Padres organization to be killed in a car crash in less than year.
On July 29, minor league pitcher Gerik Baxter was killed near Indio, Calif., when a rear tire on his pickup blew out, causing the truck to swerve into another car and roll several times. Oakland Athletics draft pick Mark Hilde, a passenger in the truck, also died.
Darr is survived by his wife, Natalie, and two sons, Mike Jr. and Matthew.