ST. LOUIS -- Though each has a different circumstance, both Daniel Mengden and Beau Taylor’s long-term roles with the A’s are cloudy at best.

Each player made a strong case for an extended stay in Oakland’s 2-0 win over the Cardinals on Wednesday night as the A’s swept the two-game Interleague series.

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Mengden was recalled before Wednesday’s game to join the rotation in the place of Frankie Montas, who was suspended for 80 games on Friday for a violation of MLB’s performance enhancing drug policy. The right-hander scattered four hits, all singles, through six scoreless innings. He struck out five and walked one.

“I know I belong here and I can pitch here,” Mengden said. “It’s really tough to hear what happened to Frankie. It’s kind of one of those things where we’ve always been next man up.”

The only sign of trouble Mengden (2-1) saw came in the sixth after Paul Goldschmidt singled, when he walked Marcell Ozuna with two outs. But Mengden got Jose Martinez to roll over on a slider to ground out, ending the threat.

“He was terrific and we’ve been talking with him about this for awhile,” A’s manager Bob Melvin said. “When he finds a rhythm and his timing, stick with it. He was quick to the plate every time there was somebody on base. He had the same delivery, the same times, and he was throwing the ball where he wanted to throw it.”

Mengden continued his dominance in Interleague play, winning his fourth straight start against the National League dating back to Sept. 15, 2017. It was his third scoreless outing during that span.

“It might just be the way he’s pitching at the time,” Melvin said. “That plays against anybody the way he pitched today.”

The performance was a marked improvement from Mengden’s first stint with the A’s this season, in which he went 1-1 with a 5.09 ERA in five appearances. The difference was his ability to control counts and limit his pitch count.

Mengden started 17 of the 23 batters he faced with a first-pitch strike.

“Me and Beau had a great game plan going in, keeping the ball down really good,” Mengden said. “I think we were throwing really good pitches and had a really good pitch call in certain situations, whenever we were ahead, throwing certain pitches off of the plate and getting them to chase.”

Mengden and Taylor’s chemistry was forged the past few years in the A’s Minor League system. They have been teammates, moving up the system together from Class A Advanced to the Majors.

“He did an outstanding job coming in right from the get-go, pounding the zone and keeping the ball down and working his offspeed in there for strikes and just keeping them off balance,” Taylor said.

Taylor’s 398-foot home run into the right field bullpen off of Adam Wainwright (5-7) broke a scoreless tie in the fourth inning to give Mengden the early advantage. It was the 29-year-old’s second big league homer.

Taylor was selected from Triple-A Las Vegas on June 8 and has carved out a role backing up Josh Phegley behind the plate. He has four hits in his last 14 at-bats with two homers, two RBIs and two runs scored.

“I’m just trying to have competitive at-bats out there,” Taylor said. “I don’t want to get up there and they see me as a guy who gets called up, a light hitter, and he’s going to be an easy out. I don’t want to be that at all.”

But with catcher Chris Herrmann on a rehab assignment at Las Vegas working his way back from right knee surgery, Taylor’s future with the big league club is murky, and he is making his case with his play.

“He hasn’t been here that long,” Melvin said. “We’ve seen him get all of the firsts out of the way, and now really delivers in a big game where runs were at a premium and not only catches a shutout -- which you should be really proud of as a catcher -- but contributes with a home run. Good day for Beau.”

Yusmeiro Petit and Joakim Soria pitched a scoreless seventh and eighth respectively, before Liam Hendriks earned his second save since closer Blake Treinen was placed on the 10-day injured list with a strained right shoulder last week.

Matt Chapman added a solo homer in the seventh, extending his on-base streak to 12 games. The A’s hit five homers in the two games at Busch Stadium.

Oakland has won 10 of its last 14 games and is a season-high five games above .500.

“I think it’s just important to take the momentum from this series into tomorrow’s game and leave it at that, and go out with the expectation to win,” Melvin said.