By Bruce Levine–

CHICAGO (CBS) — The Cubs took a big step in fortifying their bullpen Wednesday, trading minor league slugger Dan Vogelbach to the Mariners for left-handed reliever Mike Montgomery.

After being used as a starter and reliever by Seattle in the past two years, Montgomery will pitch out of the bullpen exclusively this season for Chicago, president of baseball operations Theo Epstein said.

“We have been looking hard to improve the pen if we could,” Epstein said. “We were especially looking for a left-handed pitcher. Montgomery has really good stuff. He has been performing well this year. We really feel he is coming into his own. We really think this was a fair deal. He has a chance to help us this year and long into the future.”

Montgomery, 27, could get an opportunity to join the Cubs starting rotation in 2017, Epstein said. For now, the hard-throwing Montgomery will try to fit into the left-handed setup role to complement right-hander Pedro Strop and closer Hector Rondon. Montgomery has a 2.34 ERA and 1.09 WHIP in 32 appearances this season. He’s under club control through 2021.

A second-round pick in 2011 by the Cubs, the 23-year-old Vogelbach has batted .290 with 76 home runs and 323 RBIs in 500 career games in the minors. He hit .318 with 16 homers, 64 RBIs and an .875 OPS in 89 games at Triple-A Iowa this season.

This deal won’t stop the Cubs from going after other top relievers who are apparently on the trade market, Epstein said. The next 11 days before the non-waiver deadline for deals passes on Aug. 1 will find the Cubs in many discussions to add more quality players

“Deals like this are not always about the right now but also the future,” Epstein said. “We needed to add controllable pitching (Montgomery has five years of control left). We need to look ahead. You just can’t build your pen and rotation one offseason at a time. We have done a much better job adding position players than pitching. We needed to fill that void.”

Montgomery was selected in the first round by the Royals in 2008. He was dealt to the Rays in late 2012 in the blockbuster James Shields-Wil Myers deal, then went to the Mariners ahead of the 2015 season in another trade. The 6-foot-5 Montgomery made his MLB debut in 2015.

Now, he’ll be counted on by a Cubs team with championship dreams.

“He had a lot of prospect status and has had to fight through a longer development path,” Epstein said. “I think left-handed pitchers do take a little bit longer to develop. These longer-limb lefties, their command takes longer to come around.”

Montgomery has struck out 54 batters in 61 2/3 innings this season. Left-handed hitters have batted just .164 against him.

The sweepstakes for the two studs in the Yankees bullpen should take off in the next few days. With that in mind, don’t count the Cubs out of the mix for Aroldis Chapman and Andrew Miller. Epstein has already acquired Miller once in his career, back when he was the Red Sox’s general manager.

Regardless of how that plays out, Epstein was happy to improve his bullpen Wednesday.

“I like making this kind of a move early,” Epstein said. “We have not touched certain parts of our prospect inventory. That will keep us very viable for every opportunity that is still out there. I feel good about doing something you like, so you have something to fall back on. It gives you the ability to say no and draw a line. We have not touched the prospects we potentially are going to move in some bigger deals in the future.”

Bruce Levine covers the Cubs and White Sox for 670 The Score and CBSChicago.com. Follow him on Twitter @MLBBruceLevine.