The Oakland A’s on Thursday morning acquired Boston Red Sox starter Jon Lester, the playoff-tough left-hander who can be a free agent at season’s end, in an all-in effort to win the AL West and make a deep October run.

The addition of Lester comes 26 days after the A’s acquired ace right-hander Jeff Samardzija from the Chicago Cubs, and so they have remade the top of their rotation. They already had Sonny Gray and Scott Kazmir.

The agreed-upon trade will send Lester and outfielder Jonny Gomes to the A’s. In return, the Red Sox, embarking on their second roster makeover in two years, receive outfielder Yoenis Cespedes and, critically, a competitive balance pick in the 2015 draft. Cespedes, 28, can become a free agent after the 2015 season. In his third major league season, Cespedes is batting .256 with 17 home runs and 67 RBI.

Gomes, 33, played in Oakland in 2012. He'll mix in with the platoon-heavy A's in the outfield.

The Red Sox acquired the second pick in what is known as "competitive balance round B," which will come after the second round of the draft.

Boston also is expected to attempt to move pitcher Andrew Miller by the deadline.

The A’s completed another trade Thursday, sending 27-year-old left-hander Tommy Milone to Minnesota for outfielder Sam Fuld. Fuld, 32, played seven games for the A's earlier this season before being placed on waivers.

A year ago Lester was pitching the Red Sox toward the postseason in what would become one of the unlikeliest World Series championships in history.

The Red Sox had finished last in the AL East in 2012, in part because Lester lost 14 games and posted a 4.82 ERA, both career worsts. The organization also had broken apart under manager Bobby Valentine, the symbolic worst being reports of in-game beer-and-chicken clubhouse gatherings during games. Lester had been part of that group, along with fellow veterans Josh Beckett and John Lackey. At season’s end, Valentine was fired and the Red Sox rebuilt for 2013. Lester, like the rest of the Red Sox, rebounded.

He was 15-8 and lowered his ERA by more than a run. He won four postseason games, including two in the World Series against the St. Louis Cardinals. In those two World Series starts, Lester allowed one run in 15 1/3 innings. Six years before, Lester, then 23, started and won the deciding Game 4 of the 2007 World Series in Colorado.

While the enigmatic Red Sox have returned to last place in ’14, Lester is pitching as well as he ever has. Through 21 starts, he is 10-7 with a 2.52 ERA, fifth-best in the American League. In eight starts since early June, his ERA is 1.07 with 54 strikeouts and nine walks.

Lester is again among the best starting pitchers in the game. At 30, he also is due to become a free agent at the end of the season. The Red Sox attempted to low-ball Lester in the spring, offering him a four-year, $70 million contract extension. That was rejected. Subsequent negotiations went nowhere.

So, with the Red Sox having lost seven of eight games leading to the trading deadline and falling further into the AL East basement, they decided to add Lester – along with Lackey – to a trade market thirsty for pitching.

For what amounts to a rental of two months plus whatever comes in October, the Red Sox engaged most of the league’s contending teams, including the Cardinals, Baltimore Orioles, Los Angeles Dodgers, Pittsburgh Pirates, Oakland A’s and, for a time, Milwaukee Brewers.

The market bore other available aces, potentially complicating those talks. The Tampa Bay Rays offered 2012 Cy Young Award winner David Price, while 2008 Cy Young Award winner Cliff Lee and Cole Hamels were available from the Philadelphia Phillies.

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