ST. LOUIS -- Young shortstop Jose Barrero didn't know exactly when he would get the chance to help the Reds but he knew it could happen at any time. Barrero was called up Monday to join the road trip in Chicago as a taxi-squad member, and he had to be ready whenever regular shortstop Kyle Farmer's wife was ready to have a baby.

Farmer left for paternity leave Friday and Barrero stepped in -- and then stepped up. He scorched an RBI double for the go-ahead run and scored another run during the Reds' 4-2 series-opening victory over the Cardinals at Busch Stadium.

"I was definitely getting my work in, my training in while I was on the taxi squad, but I was just waiting for the opportunity to get the call. Fortunately enough, I got that today," Barrero said through translator Jorge Merlos.

Cincinnati picked up a game on San Diego for the second National League Wild Card spot, pulling into a tie once again after the Dodgers defeated the Padres on Friday night.

In the bottom of the eighth with Michael Lorenzen pitching in a 2-2 game, Barrero made a two-out fielding error when he charged Tyler O'Neill's ground ball and mishandled it. Lorenzen escaped unscathed.

In the top of the ninth against St. Louis reliever T.J. McFarland, with Aristides Aquino on first base, Barrero opened with an 0-2 count before taking a trio of pitches. McFarland's 3-2 pitch was scorched to the left-center-field gap and bounced once before hitting the wall.

"I was just very concentrated on the at-bat," Barrero said. "I knew that the team had to win tonight, so I really wanted to get my best at-bat that I could."

"It was a mature at-bat and a big at-bat, a big hit," Reds manager David Bell said. "I think if anything, it's great to get him in and feeling like he's contributing to this team. We know how good of a player he is. We know how talented he is and he's going to play in this league for a long time."

Waved around by third-base coach J.R. House, Aquino scored as the cutoff throw was wide of the plate. It allowed Barrero to take third base on the play, which proved pivotal.

"It was a great send by J.R.," Bell said. "Aquino got his momentum going between second and third pretty well. Once he gets going, he can really run."

When the next batter, Delino DeShields, grounded to short, Barrero bolted for home on contact and beat the throw to the plate with a headfirst slide.

Barrero, 23, was promoted from Class A-Advanced to the big leagues in 2020 because there was no Minor League season and the club thought his glove was ready. His bat predictably lagged behind in adjusting to Major League pitching and he batted .194 with 26 strikeouts in 67 at-bats. Given a six-game callup last month, he was 2-for-12 with a double on the season entering the night.

But Barrero's lively bat -- his double had an exit velocity of 102.9 mph -- has many believing he could be a formidable hitter with more experience.

"I just want to say it was a great opportunity for that young man as a rookie to come up there and have that opportunity to help us win a game," said reliever Mychal Givens, who pitched the bottom of the ninth for his seventh save. "That’s going to be a really big moment for him. Hopefully he remembers that big moment and continues to play off of that.”

Cardinals lefty Jon Lester gave up two runs over seven innings -- both on homers. With one out in the top of the second inning, Eugenio Suárez hit his 26th home run of the season by crushing a 2-2 pitch to left-center field. There was one out in the fourth inning when Joey Votto -- on his 38th birthday -- slugged the first pitch from Lester to left-center field for his 30th homer of the season and a 2-0 Cincinnati lead.

Reds starter Tyler Mahle endured one shaky inning and it cost him his lead. Following a four-pitch walk to leadoff batter Nolan Arenado in the fourth inning, Yadier Molina hit a game-tying two-run homer to left field. Molina was fired up as he rounded the bases, bringing the crowd to life.

But Mahle -- who had 83 pitches through four innings -- helped extend his outing by getting efficient and retiring his final seven batters in a row. He needed only five pitches in the fifth inning and eight more in the sixth before exiting with his road ERA this season at 1.97 -- compared to 6.09 at Great American Ball Park.

"It was a huge game for us to start the series," Mahle said. "I’m glad I was able to contribute and help us win."