The Mets announced the deal minutes before a 6-0 loss to Atlanta. Davis, 27, was on the field during batting practice earlier in the day.
The Pirates had searched all winter for a first baseman, without success in the trade and free-agent markets. Davis hit 32 homers for the Mets in 2012, but fell off sharply last year. He was hitting .208 with one home run and five RBIs in 24 at-bats this year.
Harang pulled during no-hit bid
Aaron Harang did not allow a hit over seven innings for Atlanta but was pulled after 121 pitches, and the Mets broke up the Braves' no-hit bid when David Wright singled off reliever Luis Avilan with two out in the eighth.
As Harang's pitch count increased on a chilly evening, it seemed doubtful Manager Fredi Gonzalez would let him go the distance. Harang worked around six walks, including two in the sixth inning and two more in the seventh, before leaving for a pinch-hitter during a long, four-run eighth. Jordan Walden completed the combined one-hitter.
Cincinnati closer Aroldis Chapman was cleared to throw batting practice for the first time since he was hit in the face by a line drive during an exhibition game on March 19. Reds Manager Bryan Price said Chapman probably would throw during a 10-game trip that ends April 27. . . . Toronto shortstop Jose Reyes, who hasn't played since straining his left hamstring during his first at-bat of the season on March 31, will be activated Saturday, the Blue Jays said. . . .
Oakland signed left-handed reliever Sean Doolittle to a five-year contract that contains club options that could extend the agreement through the 2020 season. Financial terms weren't disclosed. . . . Texas starting pitcher Tanner Scheppers is headed to the disabled list with elbow inflammation. . . .