"He'll spot start," manager Clint Hurdle said. "Plays all four infield positions and both corners of the outfield. He is a right-handed bat with some barrel. I think we got better with his addition."
Nix, then, essentially is Josh Harrison 2.0. The original now becomes the everyday third baseman, as the club considers the immediate future of a struggling Pedro Alvarez.
Nix was a No. 1 pick by Colorado in the 2001 First-Year Player Draft -- he broke in playing for Hurdle's Rockies in 2008 -- and becomes the seventh former first-round choice on the current 40-man roster.
The younger brother of Laynce Nix, Jayson played 18 games with the Phillies earlier this season and was batting .274 in 54 games with Durham, the Rays' Triple-A affiliate in the International League.
"I'm pretty comfortable pretty much everywhere I play," Nix said. "I'm aware this club has been playing well, and I'm very excited to join a team that's in the race."
To clear room for Nix on the 25-man roster, Brent Morel was optioned to Triple-A Indianapolis in the wake of his three-RBI game in Saturday night's 8-3 win over the D-backs. Infielder Dean Anna, claimed on waivers from the Yankees a month ago, was designated for assignment to open a spot on the 40-man roster.