How have the Chicago Cubs slipped in the NL Central? Jet lag, air pollution, rain delays — and a breakdown in all 3 phases of the game.

MILWAUKEE — The Chicago Cubs scored four first-inning runs against the St. Louis Cardinals in the second game of the London Series on June 25, looking to get back to .500 for the first time since May 12.

With 11 wins in their previous 13 games and Marcus Stroman on the mound riding a seven-game win streak, it looked like the Cubs finally had turned a corner in a season that began with so much promise before hitting a wall in late April.

The Cubs were trying to buck history. A 12-26 stretch that began the final weekend of April had left them 10 games under .500 after a sweep by the Los Angeles Angels in Anaheim on June 8. Only two teams in franchise history were able to fight back to .500 after being double-digits under the breakeven mark.

If the 2023 Cubs were to become the third, it would go down as an inspiring comeback story for a veteran team led by newcomers like Dansby Swanson, Cody Bellinger and Trey Mancini — all of whom were brought here in part for their championship experience.

But a few defensive misplays at first by Mancini started the Cubs’ downfall, and the Cardinals stormed back to take the lead in London. Stroman was removed in the fourth inning with a developing blister on his right index finger and was charged with six runs (three earned) on nine hits in a 7-5 loss that sent the Cubs home with a split.

Despite a missed opportunity, the Cubs were in good spirits when they arrived back at Wrigley Field two days later for the start of a six-game homestand against the Philadelphia Phillies and Cleveland Guardians. It would be a chance to get back over .500 before a crucial four-game road series against the Milwaukee Brewers in July.

An air quality alert stemming from the Canadian wildfires threatened to postpone the first game, with Chicago having the worst air pollution in the world, deemed “very unhealthy” by the EPA.

But MLB decided after conversations with the Players Association that the show must go on.

The Cubs lost 5-1 to the Phillies in a haze, and the postgame discussion in the clubhouse was about how the league decided to play in the first place.

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“You smell it, you taste it, but you just go out and play baseball and forget about it when you go out there,” Cubs player rep Ian Happ said.

Happ didn’t know what went into MLB’s decision, but league sources told the Tribune it was made after consulting with multiple medical experts, weather forecasters, the teams and medical staff of both clubs.

The air quality was marginally better the next day, but Drew Smyly allowed seasons highs of seven runs and nine hits in an 8-5 loss. The Cubs offense was lifeless the following day, as the Phillies won 3-1 to sweep the series.

There was no reason to panic. The Cubs were still only five games back in the National League Central, a division no one seemed anxious to win. A 10-1 win over the Guardians on the final day of June provided hope the worst was behind them. The Cubs finished June with a respectable 14-11 record, a far cry from their 10-18 performance in May.

But July started out poorly.

After a long spring drought, the skies opened up Saturday, leading to a nearly three-hour delay of the start of the nationally televised game against the Guardians. Fox Sports reporter Ken Rosenthal said on the broadcast the Cubs would not negotiate an extension for Stroman before the Aug. 1 trade deadline — despite the pitcher’s lobbying on Twitter — leaving the option open to trading their star if the team fell out of contention.

Stroman’s blister issues were behind him, but he suffered his second straight loss as the Cubs lost 6-0 in a game that ended near midnight. Most Cubs fans were sleeping by the end of the game, just like the lineup.

Sunday morning began with a deluge, and the Cubs made an early decision to push back the starting time three hours to 4 p.m. to avoid the worst of the storm. Another two-hour delay ensued, making for another long day at the ballpark.

The Cubs offense was shut down again, entering the ninth inning trailing 6-2 with only three hits. But Mancini’s single ignited a four-run rally that saw the Cubs come back and tie the game. It was the first time since a 7-6 win over the Cardinals on July 20, 2021, that the Cubs scored four or more runs in the ninth to tie a game or take the lead.

But what could’ve been a momentum-shifting win fell by the wayside when the Guardians scored a pair of runs off closer Adbert Alzolay in the tenth inning, giving Cleveland an 8-6 victory and ending the homestand at 1-5. The Cubs had lost three games in the division standings since their opening win in London, and now trailied the Brewers and Cincinnati Reds by six games.

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The sun came out again Monday in Milwaukee, and the Cubs responded with six early runs in the opener of the crucial series against the Brewers. Smyly issued a one-out walk to the No. 9 hitter, then three straight run-scoring hits as the Brewers cut the deficit to three runs. A pair of leadoff walks by Smyly led to his early departure in the fourth, and the Cubs bullpen that had paved the way for their June revival frittered away the lead with three walks in a three-run seventh.

The Cubs wound up with an 8-6 loss, their seventh in eight games, falling seven games behind the coleading Brewers and Reds while also losing Nick Madrigal to a hamstring injury. They’ve hit a combined .238 with a .653 OPS in that eight-game stretch, while Cubs pitchers have posted a 4.94 ERA. That’s not going to make them “buyers” at the trade deadline.

With the long flight to and from London, jet lag, air quality issues and long rain delays, the Cubs seemingly ran into one obstacle after another. Reliever Michael Fulmer called the rest of the Brewers series “must-win” games, while Swanson said the Cubs needed to “man up” and own it without looking for excuses.

Kyle Hendricks takes the mound Tuesday in Milwaukee as the Cubs try to even the series on the Fourth of July and get back in the race.

How they respond to their latest adversity could determine the makeup of the team the final two months of the season and beyond.