John Smoltz has reached preliminary agreement on a contract with the Boston Red Sox, who also agreed Thursday to a one-year contract with outfielder Rocco Baldelli.

A person familiar with the negotiations, speaking on condition of anonymity because the final paperwork had not been completed, said Smoltz will sign a guaranteed deal with the Red Sox worth about $5 million and also have the possibility of earning another $5 million in performance bonuses. The deal was expected to be finalized later Thursday.

Smoltz, the only pitcher in baseball history with 200 wins and 150 saves, had pitched for the Braves since 1988. The 41-year-old is coming off major shoulder surgery that sidelined him for most of last season, but feels healthy enough to pitch at least one more year.

The deal, which also was reported by several other media outlets, means that Smoltz will likely finish his career with a team other than the Braves — a startling development given his long history with the team. He was an unknown minor leaguer when acquired from Detroit in 1987 for Doyle Alexander, but went on to become a cornerstone of Braves’ teams that won a record 14 straight division titles from 1991-2005.

Smoltz apparently turned to the Red Sox after the Braves balked at giving him more than a $3 million deal, the person said. Atlanta general manager Frank Wren declined comment when reached by e-mail, and there was no immediate comment from Boston officials.