Another long day for Matt Kemp and Dodgers in 5-2 loss to Cardinals

What the St. Louis Cardinals did Sunday at Dodger Stadium would have been unthinkable in April.

With two outs, first base open and the score tied in the 10th inning, reliever Fernando Salas intentionally walked Andre Ethier and pitched to Matt Kemp.

Kemp flied out to center. The threat was over.

Two innings later, John Ely was charged with three runs in a brutal 12th inning for the Dodgers, who fell to the Cardinals, 5-2, and dropped one game back of their visitors for the second of two wild-card positions.

“We definitely missed a lot of opportunities to win the game,” Kemp said, pointing specifically to his 10th-inning at-bat.

Kemp is rarely hitting at all these days, regardless of the situation.

He is batting .113 since he injured his left shoulder crashing into a wall in Colorado on Aug. 28.

He has three extra-base hits in his last 13 games — one home run and two doubles, one of which came in the sixth inning Sunday. He has struck out 17 times over that span.

“I’m going up there, I’m grinding, I’m trying to get things done,” Kemp said. “But right now, I’m swinging at bad pitches and not letting the game come to me. I just have to slow down a little bit.

“I mean, guys, I know how to hit. I promise you: I know how to hit.”

Kemp said he no longer feels any pain in his left shoulder. But he made similar declarations a week earlier, only to have to be administered a cortisone injection and miss two games.

Healthy or not, Kemp’s lack of production is a major problem for the Dodgers.

Even after the Dodgers acquired such All-Star-caliber hitters as Adrian Gonzalez and Hanley Ramirez, Kemp has remained the team’s offensive centerpiece and spiritual leader. His average has fallen from .337 on Aug. 28 to .302.

With Kemp still slumping, the Dodgers are set to embark on a three-city, nine-game trip that could determine whether they make the playoffs.

The Dodgers will travel to the East Coast on Monday and start a three-game series against the Washington Nationals the next day. The Nationals have the best record in baseball.

From Washington, the Dodgers will go to Cincinnati to face the NL Central-leading Reds.

The trip concludes with a three-game series in San Diego against the Padres, who have the NL West’s best record since July 1.

The Dodgers could be punished for their failure to pass the Cardinals in the standings over the last four days.

Of the Cardinals’ next nine games, six are against the Houston Astros. The other three are against the Chicago Cubs. The Astros have the worst record in baseball. The Cubs are the only other team with a winning percentage of less than .400.

Considering the caliber of opposition the Dodgers will be facing in the next week, they can’t have the kind of offensive performances they had Sunday and expect to gain ground on the Cardinals.

The Dodgers were one for eight with runners in scoring position.

Shane Victorino was 0 for 6. Before Salas intentionally walked Ethier in the 10th inning, Victorino was at the plate with one out and men on the corners. He hit a grounder to second base that resulted in Mark Ellis being thrown out at the plate.

Adrian Gonzalez was 0 for 5. Kemp was one for five.

The only high-profile Dodger who is hitting well these days is Ethier, who is batting .345 over his last 23 games. He has hit seven home runs, including a two-run shot in the third inning Sunday, and driven in 15 runs over that span.

dylan.hernandez@latimes.com