The Yankees have reached an agreement with Richie Sexson on a pro-rated contract for the rest of the season, The Post has learned.

The Yankees are going to wait to announce his acquisition until at least before Friday night's game. But he is being added as a way for the Yanks to increase their righty presence against lefty pitching, and so he almost certainly will start tomorrow when Oakland sends out southpaw starter Greg Smith.

Sexson was released on July 10 by Seattle and the Yankees expressed interest relatively quickly. The big righty hitter was batting .218 this year, but was hitting .344 against lefty pitching with five homers in 64 at-bats, which is what made him attractive to the Yankees. He essentially will assume the role that the Yanks envisioned Shelley Duncan playing this year: The hulking righty swinger who could do some damage against lefties, in particular.

Duncan failed in the majors then injured his shoulder in the minors and was lost for the season.

Sexson is making $14 million this season in the final year of a multiyear deal with Seattle. The Yanks have to pay Sexson the pro-rated portion of the minimum salary, or roughly $160,000, for the rest of the year.

Sexson, 33, had 11 homers this year with 30 RBIs and 76 strikeouts in 252 at-bats.