BOX SCORE

CHICAGO — The Cubs began a series against the New York Mets on Tuesday with more at stake than they probably would have liked. 

After clinching a coveted postseason berth on Wednesday in Pittsburgh, the Cubs went to Cincinnati with the opportunity to seal home-field advantage in the NL Wild Card Series. Instead, they were stunned by the Reds, who swept the visitors in a four-game set bookended by 1-0 wins. 

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Four straight losses meant the Cubs have work to do if they want Wrigley Field to be the site of their first playoff action in five years, and it starts with getting back in the win column on this final homestand.

At first, they seemed to be well on their way. A 6-1 lead in the fourth inning provided that sense of security.

But then, that suddenly wasn’t the case. The Mets clawed all the way back as the Cubs blew a five-run lead — the largest blown lead of the season — and dropped their fifth straight game in a 9-7 loss.

The Cubs’ magic number to clinch home-field advantage still stands at four. They hold a two-game lead over the San Diego Padres, who are hosting the Milwaukee Brewers Tuesday night.

Here are three things we learned:

Trouble in paradise

In what was likely his final start before the playoffs, Cade Horton took the ball on Tuesday night against the team he faced in his MLB debut four months ago. 

Since that debut, Horton has broken out as one of MLB’s best young arms. On Tuesday, he had an opportunity to plug the gaps and get the Cubs back on track awaited him.

Things got a little rocky for the rising star when Mets shortstop Francisco Lindor drew first blood almost instantly. He took Horton deep on the second pitch of the game to give the Mets life in their own playoff race, as they teeter on the edge for the final NL Wild Card spot in a battle with the Reds. 

Horton allowed a single to Juan Soto in the very next at-bat, but the rookie right-hander settled in to get three quick outs and limit the damage to just the one run. 

Two straight 1-2-3 innings followed for Horton, meaning he set down nine straight following Soto’s single. But just when it started to become rhythmic for the 23-year-old, he left the game. 

Michael Soroka began warming up in the bottom of the third inning, and by the time Cubs hitters were retired, the reliever was running out of the left field bullpen door and onto the mound to take over. 

The Cubs later shared that Horton exited the game as a precaution because his back was tightening up. 

He had thrown just 29 pitches through three innings — 23 of them for strikes — while tallying two strikeouts and no walks. 

Horton’s excellent second half has been a strong case to put the ball in his hands in Game 1 of a playoff series, but a lasting injury to the NL Rookie of the Year frontrunner would derail those plans completely.

One big mistake 

When the top of the fifth inning began, the Cubs had all the momentum. 

The hosts were carrying a 6-1 lead with the bottom of the Mets’ order due up, and Soroka had worked a quick scoreless frame in the previous inning. 

But things began to unravel when Mets catcher Francisco Alvarez stepped up to the plate. With one man on and one away, Alvarez hit a sharp chopper to Dansby Swanson, at which the Cubs’ shortstop chose to charge. 

Swanson’s decision was a grave one — the ball evaded his glove and skipped into the outfield, putting runners at second and third for the Mets. Had he sat back to field the ball, he likely could have gotten Alvarez — who doesn’t run very well — out at first and instead give the Mets a man on second with two outs. 

The floodgates then opened for New York, who pushed across a run on a Francisco Lindor RBI groundout to make it 6-2. Juan Soto walked, and then Pete Alonso hit a 112-mph, 372-foot single off the right field ivy and it was 6-3. 

Then, one swing from Brandon Nimmo tied things up in front of a stunned Wrigley Field crowd. 

All five runs that New York put up in the frame were unearned as a result of Swanson’s error. 

Super sub Santana

Despite their post-clinch skid, the Cubs will still be playing in a Wild Card series — that much is factual. 

Where it will be, when it will be and who will be on that roster next week is still up in the air, but the Cubs could be seeing some of their bench pieces fall into place in this final homestand. 

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One of those is veteran Carlos Santana, whom the Cubs signed on Aug. 31 as a solid defensive replacement and a switch-hitting bat. 

The 39-year-old first baseman has plenty of playoff experience in his 15-year career, and manager Craig Counsell has used him as an option against lefties in place of Michael Busch, who struggles in those situations. 

Santana had a rough, 0-for-16 start to his Cubs tenure, but on Tuesday night, he gave the Cubs two runs via an RBI double off Mets southpaw David Peterson. It was his first pair of runs driven in on the North Side, and it perhaps provided a look into why the Cubs would want him available in the postseason.