CHICAGO -- Nico Hoerner worked through a dozen pitches from Brewers closer Josh Hader with an aggressive approach. The last seven were fouled off, sprayed around Wrigley Field, as the count remained full with the game on the line.

Finally, Hoerner lined the 13th pitch he saw to center field, where Avisaíl García made the catch to put the final touches on a 6-5 loss for the Cubs on Sunday afternoon. It marked the third consecutive defeat for a Chicago team that is encountering its first real test of this 2020 campaign.

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"I felt comfortable. I felt confident," Hoerner said. "I expected to have success there. Move on. Nothing to really change."

Those last two comments summed up the Cubs' collective approach to this series.

After a string of three one-run losses -- games that could have swung in either direction with a bloop here or there -- Chicago's players felt there was nothing to do but turn the page quickly. That is especially important given what's on-deck: Five games in three days against the rival Cardinals.

That said, this latest loss was also a kind of microcosm for the Cubs' season through this point. Chicago was up, 3-0, in the first inning, and then things got complicated. The North Siders rattled off 13 wins in the first 16 games, representing the best start for the franchise since 1907. And now, things are complicated.

The next three days may say something about this Cubs team.

"Every day says something about us. I think it's not just the next three," said Cubs lefty Jon Lester, who gave up five runs between two homers in his six innings. "The fight's there, the energy's there."

It will have to be there during this next stretch, too.

Kris Bryant has played through a series of small bumps and bruises this year -- most recently a left wrist issue stemming from a diving catch attempt on Thursday -- and he is in a 3-for-19 slump. Javier Báez was out of the starting lineup on Sunday for a mental and physical break, and he is now in an 0-for-17 funk after a groundout against Hader in the ninth.

Outfielder Jason Heyward was scratched from Sunday's lineup pregame due to mid-back tightness. A similar setback cost Tyler Chatwood a start on Friday, leading to his placement on the 10-day injured list on Sunday. That caused a chain reaction on the pitching staff.

In a short season, those kinds of nicks and slumps have created a balancing act for first-year manager David Ross.

"Every game matters, right?" Ross said. "The main thing to balance is the health of the players. I think keeping those guys fresh and competitive and watching their at-bats and their body language and how they're moving around, I think that's the main thing."

The Cubs know No. 1 starter Kyle Hendricks is taking the ball in Game 1 of Monday's doubleheader against St. Louis, but Ross and the team's brass were going to sit down postgame Sunday to figure out Game 2. There is also a "TBA" for one of the two games looming Wednesday.

"This is going to be a pretty good test," Cubs outfielder Kyle Schwarber said. "They might have their feet under them, but I think this is going to be a good test for us to be able to go out there and kind of show the guts. This isn't ideal, playing five games in three days."

The reason for that schedule stems from St. Louis' recent setbacks with positive COVID-19 tests within their player group and staff. The Cardinals returned to the field with a doubleheader sweep of the White Sox on Saturday, marking their first games since July 29 and the start of a 53-game, 44-day gauntlet.

"That's tough. I guess it's just the story of baseball this year," Schwarber said. "With the guys over there, with some of that leadership of those guys, I'm sure that they're going to want to attack it head on. But I think it can also work in our favor, too."

Potentially working in the Cubs’ favor is the fact that they have dealt with zero COVID-19 issues among their players, have cruised to the top of the division and have found a rhythm on the field, while the Cardinals missed games.

Even on Sunday, when the Brewers prevailed, Chicago's lineup pieced together a sixth-inning rally that pulled the game into a 5-5 deadlock. Veteran Jason Kipnis -- one of the bottom-of-the lineup hitters who has picked up the slumping stars -- came through with a game-tying, two-run, two-out single.

That is the fight Lester was referencing. That is why Hoerner says there is nothing to do but move on.

"A big part of this year is controlling emotion," Hoerner said. "And not letting anything feel that much more significant than it actually is. It is a shortened season and that presents a challenge, but we're lucky to have good leadership and good people in the clubhouse to make that easier to handle."