Jonathan Papelbon is closing the book on his tenure with the Boston Red Sox.
Papelbon, the longtime Red Sox right-hander who has anchored their bullpen for six years, including a World Series title in 2007, has agreed to a four-year, $50 million deal with the Philadelphia Phillies pending a physical, a source familiar with the negotiations told ESPN.com senior writer Jayson Stark on Friday.
The deal includes a vesting option that could take it beyond $60 million for the 30-year-old, the source said.
If finalized, the contract would be the largest total package ever signed by a relief pitcher. The previous high was the five-year, $47 million deal signed by B.J. Ryan with Toronto in December 2005.
The $12.5 million average annual value of the deal would be tied for the second-highest ever signed by a reliever.
Mariano Rivera's $15 million a year, in each of his last two contracts, ranks No. 1.
Papelbon's annual pay would be tied with former Phillies closer Brad Lidge, who signed a three-year, $37.5 million extension during the 2008 season, covering the 2009-11 seasons.
SportsNation: Free Agency
Papelbon takes 219 career saves, with a 2.33 ERA and 1.02 WHIP, with him to Philadelphia, despite pitching his entire career in the AL East.
It remains uncertain whether the Phillies will have to surrender their first-round draft pick next June to the Red Sox as compensation for Papelbon, because draft-pick compensation is one of the unresolved issues still on the table during the ongoing labor talks.
Under the current rules, because Papelbon is a Type A free agent, the Red Sox would receive the Phillies' No. 1 pick, the 31st overall pick, in the draft.
However, the players' union has been seeking to reduce the number of premier free agents who would require a team to surrender a draft choice. So until labor negotiations are completed, neither team can be certain of the new definition of players who would still require compensation.
Nevertheless, a source familiar with the labor talks predicted Friday that Papelbon is still likely to be among the elite free agents who would cost their team a No. 1 pick.
The deal comes after the Red Sox said they would like to re-sign Papelbon, and the Toronto Blue Jays and Florida Marlins reportedly also had expressed strong interest.