That left the Cardinals losers in eight of their last 10 and with a manager uninterested in providing much detail after an obviously frustrating conclusion to a nightmarish West Coast swing.
"Good chance right there," Matheny said. "We needed that one."
It's not just the losses that are cause for concern, but the way in which games have recently unraveled. The bullpen has been scored upon in 12 of the team's last 13 games, and the club has had just one seven-inning start since May 9. In that span, the defense has accumulated 10 errors.
"We're going through a little bit of a tough spot right now," said Marc Rzepczynski, Van Slyke's victim. "The starting pitching, the defense, it just depends on the night. We're in a little bit of a funk all around."
And it's the injuries. Since leaving St. Louis last Tuesday, the Cardinals have had to place three key players -- Allen Craig, Lance Berkman and Kyle McClellan -- on the disabled list. The latter two could be lost for months.
"You look at what we're having to deal with as far as injuries and it's just tough right now," said Sunday's starter Kyle Lohse. "You ask anybody to go out there and get it done with as many missing parts as we have, it's tough. We're just not playing good. I don't know how to put it. I'm not going to make any excuses. We just have to do a better job."
This was the third time in their last six series that the Cardinals have been swept, and they leave Los Angeles with a tenuous hold on their National League Central lead. That advantage is now a half-game over Cincinnati, the slimmest margin since April 11.
The Cardinals' 5-3 lead was the bullpen's to protect after Lohse exited with two outs in the sixth. Victor Marte closed out that inning and faced the first two batters in the seventh before handing things over to Rzepczynski.
Matheny made the move to get Rzepczynski into the game at a point where the Dodgers had four straight left-handed hitters coming to the plate.
Rzepczynski allowed one hit, struck out another, and then Dodgers manager Don Mattingly countered by pulling Adam Kennedy for the right-handed-hitting Van Slyke.
"I thought they might use somebody off the bench," Matheny said afterward. "Rzepczynski is who I'd want out there anyhow."
Though another left-handed hitter waited in the on-deck circle, Matheny said the plan was to have Rzepczynski go after Van Slyke, whose Major League resume included eight previous at-bats.
Unable to get Van Slyke to chase his sinkers, Rzepczynski fell behind. He guessed that Van Slyke would anticipate a 3-0 fastball, so he chose changeup. Van Slyke's timing was flawless and sent a crowd of 44,005 into a frenzy.
"I tried to keep it down, but it was a little bit up," said Rzepczynski. "He's got the power. I know it's his first career home run, but there's definitely a reason he was given a chance to hit there."
"I don't think he was going to pinch-hit me to walk or get a little single," Van Slyke said of Mattingly's call. "I think he wanted me to do some damage."
It wasn't all Rzepczynski's burden to bear. Looming particularly large in the loss, too, was the Cardinals' inability to capitalize on run-scoring chances early.
They had six baserunners reach in the first two innings, and none scored. A muffed double steal halted momentum in the first. A double play with the bases full ended the second.
A just-as-forgettable performance was put in by David Freese, who struck out four times in as many at-bats. He is now mired in a 3-for-34 slump, and all three hits came on one night.
"He's got some fighting to do," Matheny said.
The offense did eventually get to Dodgers starter Chad Billingsley, turning a 2-0 deficit into a three-run lead.
Billingsley's own error -- he missed first base after taking a feed from first baseman James Loney -- led to two unearned runs in the fifth. The Cardinals pushed across three runs in that frame, with Skip Schumaker delivering a two-run triple.
St. Louis tacked on two more in the sixth with Rafael Furcal's two-run single. But the Cardinals were even left to consider what could have been in that inning, too. Before Furcal's two-out knock, Yadier Molina was called out trying to advance from first to third on a single.
Replays appeared to show that he was safe.
The bullpen cost Lohse a chance for his second win this month. He allowed 11 hits, but only one went for extra bases, which allowed him to minimize the damage. That extra-base hit came on a ball misplayed by outfielder Carlos Beltran in the sixth, and it led to the Dodgers' third run.
"It was a weird, weird outing," said Lohse. "There wasn't a whole lot of really hard contact. Ground balls were just out of somebody's reach."
First baseman Matt Adams finished with two hits and a run scored in his Major League debut. Added to the roster a day after Berkman suffered a right knee injury, Adams collected a single on the first pitch of his first at-bat.
He'll have to wait at least another day for that first win.
"All we can do," Lohse said, "is what we're capable of and try to pick each other up."