PHOENIX -- Locked in a scoreless duel with Arizona ace Zac Gallen through four innings, Cardinals veteran right-hander Miles Mikolas knew his margin for error was small on Sunday at Chase Field.

Ultimately, the one-hitter Mikolas worked through the game's first four innings devolved into a forgettable 5-0 loss to the D-backs.

When Mikolas grooved a 1-2 pitch to Joc Pederson in the fifth, the Arizona DH drilled it down the first base line for a double that ignited a rally. Then, Mikolas hung a 2-2 slider to Jace Peterson for the game's first run off a sacrifice fly. Finally, Mikolas' 0-1 slider to Jake McCarthy came in elevated and the D-backs' right fielder punished it for a run-scoring double.

After walks to the following two batters, Mikolas was incredibly out of a game in which he was dominant over the first four innings. It left him trying to pinpoint where his start went so badly off the rails.

"I felt good early but lost a little there in the fifth," said Mikolas, charged with five earned runs. "A couple of singles, a chopper down the line and a blooper and I got myself in trouble with some walks. That was the end of it."

Remarkably, it was the 33rd start of Mikolas' career since he became a Cardinal in 2018 in which he got zero runs of support, per Cards PR. He said he tries to keep every inning the same -- whether he has a lead or is locked in a scoreless battle, as was the case for four innings on Sunday.

"It's the same as any outing -- I'm doing my best to keep runs off the board," said Mikolas said. "[Run support] is not something that I really think about. My job is to keep runs off the board. I didn't do that today and that's why we lost."

St. Louis has gotten above .500 just once this season and it has also been 3-3, 4-4, 5-5, 6-6 and 7-7. A big reason why the Cardinals have been unable to sustain success is their five losses in each of their five series finales. Still, it's an improvement over last season, when the Cardinals never got over .500 after a 2-1 start.

"Whether it's a series or a ballgame, you've got to win more than you lose, ideally," Mikolas said. "Something we need to do better as a team is we need to close out games and close out series."

The Cardinals squandered two golden opportunities to grab an early lead against Gallen and failed to score even when they only needed to put the ball into play. In the second inning, the Cards loaded the bases with one out, but veteran shortstop Brandon Crawford took strike three right down the middle.

At issue was rookie shortstop Masyn Winn getting another day off on Sunday even though he didn't start on Wednesday and had Thursday to rest following a team travel day. Winn, the Cards' top hitter this season at .349, had four hits, a stolen base and two RBIs in the first two games of the Arizona series, but Cardinals manager Oliver Marmol said the club is trying to keep the 22-year-old healthy over the entire season.

"Masyn needs a day," Marmol said. "We talked about it and his body can use it. He's swinging it well, playing good defense and running the bases -- he's doing everything you would want him to do. But in conversation with him, today would be a good day for him to have it off. This is going to be a long season for him and keeping him fresh will be important. Our conversation has been good, and we agreed that today would be a good day for him to rest."

In the top of the fourth inning, Willson Contreras doubled to extend his on-base streak to a career-best 20 games, and he moved up to third with one out. However, red-hot rookie catcher Iván Herrera struck out on a 78.5 knuckle curve from Gallen. The threat ended when Crawford flied out. The Cardinals had just one baserunner after Contreras' fourth-inning double and they finished 1-for-7 with runners in scoring position and left six runners stranded.

"Easier said than done," Marmol said of his team's attempt to score off Gallen. "He's a good pitcher. We're trying to put it in play, but at-bats were tough."