The Cubs are in the middle of a pennant race and in an effort to keep their bullpen fresh and to help slow down Bryce Harper and the Nationals, they’re pulling out all the stops.

They inked veteran left-hander Jorge De La Rosa to a deal Friday morning, sending rookie Randy Rosario to Triple-A Iowa and pushing Yu Darvish to the 60-day disabled list to create room on the roster. (That doesn’t mean Darvish has suffered a setback. He’s already been on the shelf more than 60 days and moving him to that list creates an opening on the 40-man roster for De La Rosa.)

They also shifted their starting rotation to briefly go to a four-man unit and roll Mike Montgomery back into the bullpen.

Montgomery just tossed 6 shutout innings in Kansas City earlier in the week and feels like he’s really turned a corner with a new curveball grip and the ascension of his changeup.

But the Cubs also want to limit the wear and tear on his arms while he’s on pace to throw a career high in innings.

Montgomery will start next Saturday Aug. 18 in Pittsburgh while Jose Quintana and Kyle Hendricks will throw against the Brewers in an all-important two-game showdown at Wrigley Field next week.

“We’re just trying to be proactive with Mike,” Joe Maddon said. “That’s all. Talking about him pitching so well and he has. We just think we want to monitor his time out there a litlte bit so that he can be effective into September.”

Maddon believed Montgomery’s confidence is “soaring” as well and called the 29-year-old left-hander “invaluable” to the Cubs for all he’s done in 2018. But now Montgomery will slot into the bullpen starting Saturday and provide another option to get the slew of Washington left-handed hitters out. 

It’s not just Harper – the Nats boast a strong supporting cast of left-handers in Juan Soto, Adam Eaton, Daniel Murphy and Matt Adams.

Harper and Soto are still very good even when facing southpaws – Harper has an .836 OPS vs. lefties compared to .897 vs. righties while Soto actually carries a higher OPS vs. lefties (1.145) than righties (.917) – but the other three are severely neutralized in splits.

Murphy’s OPS vs. lefties is .520, Eaton’s is a minsicule .347 and Adams has a .640 OPS. All three guys entered the series with an OPS at least .820 or higher against righties.

Even if it’s only for one batter over the weekend, Montgomery gives the Cubs a unique option and then can shut him down on the off-day Monday and work back up to his start next weekend in Pittsburgh.

De La Rosa also will get in a lot of work against left-handers in his initial foray into life as a member of the Cubs bullpen, Maddon confirmed.

The 37-year-old veteran has been very tough on left-handed hitters throughout his 15-year major-league career, holding them to a .231 average and .652 OPS. 

Righties have had more success against De La Rosa on the whole (.803 OPS), but that’s taken a huge jump up in 2018 – right-handed hitters are batting .324 with a .927 OPS off De La Rosa this season.

De La Rosa said he’s ready for any role with the Cubs after being designated for assignment and subsequently released by the Arizona Diamondbacks earlier this month. It’s a low-risk signing for the Cubs, who are still searching for some left-handed help in the bullpen (though they do have a bunch of righties who can attack left-handed hitters well). 

In 42 games with the D-Backs, De La Rosa had a 4.63 ERA and 1.60 WHIP, but a lot of that damage came in one outing in Colorado last month, when he surrendered 7 runs in 1.2 innings. Going into that game, De La Rosa carried a 3.00 ERA and 1.47 WHIP.

Allowing a baserunner-and-a-half per inning is not the stuff of an elite closer and taking away a reliever’s worst outing would make any pitcher’s stat line look significantly better. 

But De La Rosa could be a diamond in the rough for the Cubs as they search for another left-handed weapon in the bullpen and if not, the cost is minimal.