PITTSBURGH — Derek Shelton hates to be on the other side of that situation pregame, one of the few spots where he’ll publicly admit causes him some anxiety. It’s when a team sends out a lineup, has to scratch a player late and then substitutes someone else in.

This time, though, he was on the other end. Bryan Reynolds was a late scratch with back spasms, according to the club, and had to miss his first game of the year. That forced Shelton’s hand to put Connor Joe in the outfield and put lefty Rowdy Tellez in the lineup against Cardinals left-hander Matthew Liberatore.

“It’s either really bad or really good,” Tellez said about being a late substitution. “There’s no in between.”

“I know when people switch lineups, I’m always like, ‘Ah man, the guy that comes in, you think something good’s gonna happen,’” Shelton said. “Rowdy had a good game today.”

It went really well for Tellez, who shot the opening and closing RBI salvos in a 5-0 Pirates’ win over the Cardinals on Wednesday to take the rubber match at PNC Park.

Tellez entered the day with a .148 batting average and just one RBI against left-handed pitchers. Granted, some of that is due to a small sample size against southpaws, but his career .684 OPS against lefties entering Wednesday enforces why he’s mostly been used as a platoon. That didn’t mean he was slacking in his prep work for left-handed starters, though.

“It’s my job to show up every day,” Tellez said. “It’s not like it’s foreign to face lefties in my career, so it was just going in and understanding who was pitching and doing the homework I needed to do and being ready for it.”

That homework paid off, first in the second inning with a base hit up the middle on a two-strike slider to score Ke’Bryan Hayes and open the scoring. The Pirates’ offense, which had scored just three total runs the first two games of the series, would end up piling on four runs that frame, with Andrew McCutchen picking up a bases-loaded walk and Joe getting his first RBIs since June 11 with a two-run double.

Tellez chased Liberatore in the fourth inning, crushing a fastball and depositing it into the Allegheny River. As Tellez rounded the bases, Reynolds was seen in the dugout, pointing to the name on the back of his jersey.

“Reynolds will take credit for anything the one day he does not play,” Shelton joked.

That was more than enough offense for Martín Pérez, who vowed after his last start Friday to come back stronger. He did, tossing six scoreless frames by working around five walks and four hits. The ground ball was his best friend, including in the fifth inning when Lars Nootbaar halted a potential Cardinals’ rally with a tailor made 4-6-3 double play.

“I thought the last start he didn’t mix and match as well as he should have,” Shelton said. “He looked like he was right around the zone. I know he had five walks, but it looked like he was right around the edges, and he’s got to pitch to the edges. Sometimes it gets expanded. Sometimes it doesn’t. Today it didn’t, and he was still able to come back and execute, put the ball on the ground.”

“I’ve got confidence,” Pérez said. “It doesn’t matter. I’m always going to trust my stuff. I was able to compete with a lot of pitches in the strike zone, moved the ball. It was a great game. I was in the corners, trying to maintain so they didn’t feel too comfortable at home plate.”

The whole team is playing with an air of confidence right now, opening the second half of the season with a pair of series wins against the Cardinals and Phillies, the latter of whom has the best record in baseball. The schedule doesn’t get much easier: They have two series with the D-backs coming up, with a road set with the Astros sandwich in between. It’s some of the most important ball they’ve played in Shelton’s time as a manager, but they have showed this month that they belong to be in the thick of the playoff chase.

“We don’t give up,” Pérez said. “This is a good team, too. Continue doing good things and winning games to make the playoffs because that’s what we want.”