ST. LOUIS -- The way things are going right now, the Pirates can hardly afford to make one mistake if they want to win. And they certainly can’t make the series of fundamental mistakes they made on one game-changing play in the sixth inning of their 3-1 loss to the Cardinals on Saturday night at Busch Stadium.

“We just need to play better baseball, better fundamental baseball to put us in a position to meet the demands of the game and win at the end,” manager Clint Hurdle said.

• Box score

The game was tied at 1 heading into the bottom of the sixth after the clubs traded runs in the first. Adam Frazier launched Adam Wainwright’s first pitch out to right field for a home run, and Joe Musgrove mirrored Chris Archer’s opening frame on Friday by loading the bases with nobody out before limiting the damage to a run-scoring double-play grounder by Marcell Ozuna.

Then the wheels fell off, leading to the Pirates’ seventh straight loss, their ninth straight series defeat and their 23rd loss in 27 games since the All-Star break. Pittsburgh is now 20 games under .500 on the year.

“The way we’re playing and the way things are going for us right now, it doesn’t help us at all to sit and dwell and play the what-if game,” Musgrove said. “There’s a lot of baseball left. No one’s going to feel bad for us.”

With one out in the sixth, St. Louis' Tommy Edman swatted a double to center field. Starling Marte quickly retrieved the ball and delivered it to the cut-off man, shortstop Kevin Newman. Edman seemed intent on taking third base, but he slowed up at second and actually skipped back to the base.

Frazier held up his hands and shouted, “No, no, no,” telling Newman to hold onto the ball. But Frazier’s shout was lost in the crowd noise, and Newman uncorked a bouncing throw that skipped past third baseman Colin Moran and into foul territory. Not expecting a throw after Edman stopped at second, Musgrove wasn’t behind Moran to back up the play. As a result, the ball rolled into the Pirates’ dugout, and Edman scored on Newman’s error.

“I actually didn’t know the rule. I didn’t know if I would get third and home or just third,” Edman said. “Saw the umpire pointing me home, and I was pretty excited.”

The Pirates made three mistakes on the play, in Hurdle’s view. Newman needed to make a better throw. Moran needed to stop the ball. And Musgrove needed to back up Moran. All three players agreed with their manager’s assessment.

Said Newman: “This is the Major Leagues. You make a good throw, that doesn’t happen and he stays at second base, game continues.”

Said Moran: “I didn’t block it enough.”

Said Musgrove: “I need to be back there backing up the base. That’s my job; I’ve got nowhere else to be but there. Once I saw Edman pull up, I pulled up and I was right about on the foul line. Saw the short-hop throw, and as soon as it got away, I gave my best effort to try to cut it off, but I was a little too late. There’s no excuse for it. My job is to be behind him regardless of where the runner’s at.”

Musgrove gave up two more hits, a single to Paul Goldschmidt and a double to Ozuna, and exited the game. Lefty Francisco Liriano then came in and got Paul DeJong to put the ball on the ground, albeit in a tough spot to record an out, but Moran whiffed on a diving attempt and Newman dropped the ball while trying to throw it home. Goldschmidt scored, and the Pirates only escaped the inning when they turned an unusual 2-3-2 double play on Matt Carpenter’s bunt.

All three runs were charged to Musgrove, but it was not the first time during this tailspin -- much less this season -- that the Pirates’ defense has cost them. Pittsburgh has permitted 26 unearned runs in the first 26 games of the second half. Overall this season, the Pirates rank 27th in the Majors with a .677 Defensive Efficiency Ratio.

As Hurdle summarized the way Saturday’s sixth inning snowballed on the Pirates: “We’re getting in our own way.”

Those mistakes might not have been so glaring if the Pirates had mustered more offense against Wainwright, but they were held scoreless after Frazier’s fifth career leadoff homer. Wainwright allowed only six hits and two walks while striking out eight over six innings.

“I don’t think I’ve ever been a part of a game where, the first swing off the bat, we score a run then we don’t score another one the rest of the way,” Hurdle said. “Tough to win with one.”

The Pirates’ best chance to pull ahead came in the fifth inning, when they loaded the bases with one out and had Marte at the plate. Marte crushed a 109-mph line drive … right into the glove of a leaping DeJong for the second out. Up came Josh Bell, who took a high, inside fastball for a called third strike.

“It’s tough, man. We can’t catch a break right now,” Musgrove said. “We hit the ball hard in a lot of situations tonight with runners on base, and either hit it right at somebody or they made a good play. We had opportunities and we took the swings at the plate to capitalize on those, and the ball just didn’t fall our way.”