CHICAGO — Mike Tauchman’s wife, Eileen, had an OBGYN appointment on Thursday morning. Eileen, who’s pregnant, reminded Tauchman that the last time he delivered a walk-off hit — a solo homer on June 6 against the White Sox — they had an appointment that morning.

Eileen sent Tauchman that reminder on Thursday night — she OK’d him sharing that story — after he played the hero in the Cubs’ series-opening, 5-4 win over the Cardinals at Wrigley Field.

“I’m going to start taking her to the doctor a lot,” Tauchman quipped after hitting a pinch-hit walk-off double in the ninth inning, when Chicago rallied for three runs in the ninth inning to stun St. Louis.

The Cubs were down two runs entering the ninth. They were down to their final out multiple times, and even their final strike at several points. But they still found a way against St. Louis right-hander Ryan Helsley, one of the best closers in the Majors.

“That was fun,” Tauchman said. “It was an awesome inning. Probably one of our better innings of the year. Just really good at-bats there. It’s fun. It’s cool.”

Helsley entered Thursday tied with Cleveland’s Emmanuel Clase for the most saves in the Majors (33). He had only blown two of his opportunities this season, but the Cubs quickly showed they were not going down without a fight.

Cody Bellinger got the rally started when he hit a Statcast-projected 399-foot solo home run to left-center field with one out, cutting the Cardinals’ lead to 4-3. Bellinger, who was the Cubs’ designated hitter, came off the 10-day injured list (left middle finger fracture) on Monday, after being sidelined for 17 days and not going through a rehab assignment. He is 7-for-13 with two homers and five RBIs in three games since returning.

“[It’s] pretty remarkable, really,” manager Craig Counsell said. “One, the injury he’s coming back from is a tough one — when you have a broken finger and you feel it on kind of every swing. And two, just not having the live at-bats and stepping right back into the middle of the offense and being super productive. It’s something we’ve needed, and it’s been a big boost for us.”

Nico Hoerner kept things going two batters later, with two outs, when he hit a first-pitch single up the middle. Moments later, he made the most underrated contribution to the rally: stealing second base.

“That’s really, really hard to do [against Helsley], and that takes a lot of guts to even do something like that,” Tauchman said. “That was such a huge play for us.”

Hoerner getting into scoring position allowed him to come around three pitches later, when Swanson knocked an RBI double down the left-field line. Swanson fell behind 0-2 on a swing and miss as Hoerner stole second. He then took a slider in the dirt and fouled off another before delivering against Helsley.

Pete Crow-Armstrong was due up after Swanson, but Counsell sent Tauchman out to pinch-hit. The veteran fell behind 0-2 on a pair of called strikes but evened the count after laying off a four-seamer and a slider below the zone.

“He made two really, really good pitches,” Tauchman said. “At that point, it’s like, if it’s close, you got to put a bat on it.”

On Helsley’s fifth offering, Tauchman sliced a double down the left-field line for the game-winning hit. The Cubs swarmed him on the field in celebration, during which Tauchman’s jersey was ripped off.

“It’s a great feeling,” Tauchman said. “You always want to come through for the team. We’ve battled a lot of adversity this year, and it’s no secret we’re not where we want to be right now. This is a good start to the month. All we can do is play our best baseball right now.”

Ideally, the Cubs wouldn’t be in a position to face Helsley. But in their six matchups against him this year, they’ve fared well. The Cubs have a .414/.485/.690 slash line against Helsley, all of which are their highest totals against the 39 pitchers who have faced 25 or more Chicago hitters this season.

“We have a lot of competitive guys,” Swanson said. “We just want to go out there and do our best to get ourselves back in the ballgame, tie it up or take the lead, like we did tonight. I think that mindset, sometimes … can be the simplification of it all.

“It’s sometimes all you need, and we’ve got a lot of guys that are really, really competing night in and night out.”