NASHVILLE, Tenn. (AP) The National League champion New York Mets filled a key spot by obtaining second baseman Neil Walker from Pittsburgh for pitcher Jon Niese, and the Detroit Tigers bolstered their bullpen by acquiring reliever Justin Wilson from the New York Yankees in Wednesday trades at the winter meetings.

The Arizona Diamondbacks, meanwhile, kept upgrading their rotation. A day after finalizing a $206.5 million deal for major league ERA leader Zack Greinke, they announced their five-player swap with Atlanta that brought All-Star righty Shelby Miller and sent No. 1 draft pick Dansby Swanson to the Braves.

''Our ownership stepped up in allowing us to get Zack Greinke. It puts us in a position to get better as a team, but we weren't complete. We needed an additional piece to our rotation,'' Arizona general manager Dave Stewart said.

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Miller should slot into the No. 2 spot in the rotation ahead of Patrick Corbin, Rubby De La Rosa and Robbie Ray.

''You're getting almost 800 innings out of your starting rotation, which should help our bullpen out,'' Stewart said. ''The biggest part of our problems in our `pen last year is we had to go there very often and ask them for a lot of innings.''

Other teams are waiting for the market to develop, especially for hitters.

Among the 17 elite free agents who didn't accept qualifying offers, five had reached agreements and all were pitchers: Greinke, Jordan Zimmermann, Jeff Samardzija, John Lackey and Marco Estrada. In addition, Hisashi Iwakuma has an agreement with the Los Angeles Dodgers that remains to be finalized.

Among the remaining 11 are pitchers Wei-Yin Chen, Yovani Gallardo and Ian Kennedy, joined by first baseman Chris Davis; second basemen Daniel Murphy and Howie Kendrick; shortstop Ian Desmond; and outfielders Jason Heyward, Justin Upton, Alex Gordon and Dexter Fowler.

Davis appears set to establish the top of the batters' market after hitting 159 home runs in a four-year span. His agent, Scott Boras, is known for striking deals later in the offseason.

''In the ice-cream sandwich of markets, you have your boundaries, and then you have all the vanilla in the middle,'' Boras said. ''It's pretty hard to get to the vanilla unless you get to chocolate on the outside.''

In another trade, Seattle obtained first baseman Adam Lind from Milwaukee for right-handers Daniel Missaki, Carlos Herrera and Freddy Peralta.

The Mets got Walker a day after their No. 1 choice for a new second baseman, Ben Zobrist, signed as a free agent with the Chicago Cubs.

''We could have gone East Coast, West Coast. But I think in the end, this was the one that really motivated me the most,'' said Zobrist, the only player to appear at a news conference during the first three days of the meetings.

The 30-year-old Walker fills the hole created when playoff slugger Daniel Murphy became a free agent after New York lost the World Series to Kansas City.

''It's an exciting opportunity, obviously, with the success the Mets have had this past year,'' Walker said. ''Obviously there's mixed emotions being a born-and-bred Pittsburgher.''

Walker batted .269 with 16 homers and 71 RBIs this year.

''We view him as a real positive alternative to the deal we were looking to do the other day,'' Mets assistant general manager John Ricco said. ''He fits on a lot of different levels - a switch-hitter, he's got some power.''

The 29-year-old Niese became expendable with the development of young Mets aces Jacob deGrom, Matt Harvey, Noah Syndergaard and Steven Matz. Niese was 9-10 with a 4.13 ERA last season. A starter for years, he was shifted to the bullpen for the postseason.

The Yankees dealt Wilson, a 28-year-old lefty, to Detroit for minor league right-handers Chad Green and Luis Cessa - the latter sent by the Mets to the Tigers in the July 31 trade that brought Yoenis Cespedes to New York. Wilson went 5-0 this year with a 3.10 ERA in 74 appearances. Earlier this offseason, the Tigers acquired closer Francisco Rodriguez and right-hander Mark Lowe.

Yankees general manager Brian Cashman is willing to trade left fielder Brett Gardner and closer Andrew Miller. Cashman is confident Dellin Betances could take over as closer.

''In the right circumstances, I am open to doing business,'' Cashman said. ''It's more likely than not, because of the high (price) tags I've put out there, that we will have the same dynamic duo at the back end.''

Also:

- Major League Baseball recommended teams have protective netting between the dugouts for any field-level seats within 70 feet of home plate, both at regular-season ballparks and spring training sites.

- The playing rules committee met and talked about better protecting middle infielders and expects discussions to continue during the offseason.

- Right-hander David Hernandez agreed to a $3.9 million, one-year contract with the Philadelphia Phillies.

- Right-hander Jeff Samardzija finalized his $90 million, five-year contract with the San Francisco Giants.

-Second baseman Chase Utley completed his one-year deal to remain with the Los Angeles Dodgers.