SAN DIEGO -- For five innings on Sunday afternoon, the Padres appeared to be on their way to a sweep -- and perhaps a place back in the National League Wild Card picture.

Instead, the Rockies handed the Friars a harsh taste of reality.

Colorado capitalized on a shaky San Diego bullpen, rallying for an 8-3 victory to conclude a four-game set. The Padres will settle for taking three of four from an NL West rival. But in the big picture, that won’t be enough. Trailing by 6 1/2 games, with seven teams to jump for a Wild Card spot, Sunday was the kind of game San Diego can’t afford to lose.

• Box score

Here are four takeaways from an eventful weekend series against the Rockies:

1. The bullpen really needs some left-handed help

Dinelson Lamet was sharp through five innings, but he faced a tall task in the sixth. A righty with pronounced splits, Lamet was scheduled to face three lefties -- Charlie Blackmon, Yonder Alonso and Ryan McMahon. It didn’t end well.

Blackmon singled and Alonso went deep, tying the game and ending Lamet’s day. McMahon followed with a double off Craig Stammen, and he later scored the go-ahead run.

It's worth noting that the Padres lost Jose Castillo for the season this weekend when an MRI revealed a torn ligament in his pitching hand. In the bullpen, the Padres don’t have a left-hander who can routinely get lefties out. (Matt Strahm has been solid, but he skews much better against right-handed hitters.)

"[Castillo] gives you a distinct advantage that no one else really does," Padres manager Andy Green said Thursday, hours before Castillo sustained his injury.

Perhaps that’s why Green stuck with Lamet in the righty's third trip through the order. It’s definitely why he calls on Stammen so frequently in situations that generally call for southpaws. If the Padres are going to contend in 2020, they need to shore up their bullpen. To do so, they’ll need a healthy Castillo and perhaps another relief acquisition.

2. The Padres are getting what they need behind the plate

In mid-June, the Padres promoted Francisco Mejia and decided to give him the bulk of the playing time at catcher. He’s taken that opportunity and run with it.

Since his promotion, Mejia is hitting .336/.381/.536. Early in Mejia’s career, the Padres tried to hone his strike zone, asking him to be overly patient. Now, they’ve basically told the free-swinging Mejia to swing at what he feels comfortable swinging at.

In the second inning on Sunday, Mejia golfed a curveball below the knees into the beach area in right-center field for his sixth homer. He added a single and a double, bringing his average to .280 on the season.

“I'm swinging at pitches that I want, and pitches that I like,” Mejia said. “That's freed me up and made me more free out there when I'm playing.”

Mejia is receiving about two-thirds of the playing time right now, with Austin Hedges -- a defensive standout whose bat lags well behind Mejia’s -- getting enough reps to stay fresh as a backup. For now, the Padres seem comfortable with that type of split.

3. Manny Machado has fallen into a rare slump

Remember how scorching hot Machado was when the Padres went to Coors Field for a four-game series in June? This four-game set against the Rockies presented the polar opposite.

Machado has one hit in his last 24 at-bats, which included an 0-for-19 stretch that tied a career-long hitless drought. He snapped it with a double on Saturday night, but he went 0-for-3 with a pair of strikeouts on Sunday.

“It's just the ebb and flow of a baseball season,” Green said. “There's been a lot of hard contact on the ground that's gone at people. At the same time, you go through phases in the course of the season, and that's why you need other guys to pick you up.

“If you want to be great over the course of the year, you can't just look to one guy. He's going to be fine.”

4. The outfield rotation is working

Since they dealt Franmil Reyes to the Indians at the Trade Deadline, Padres outfielders have combined for a .301/.363/.610 slash line. Entering play Sunday, their outfield was worth 1.3 Wins Above Replacement in August, according to Fangraphs. That ranked fifth in the Majors.

On Sunday, Josh Naylor belted a solo homer to the beach area in the third. Naylor struggled in his first few big league stints. But like Mejia, he’s thriving with regular playing time.

“When you come off the bench every three days, let's say, you want to come in and make an impact right away,” Naylor said. “Maybe you get out of your swing and out of your zone. It can be tough. … Now, I feel like I'm comfortable and compact in the zone.”

In the eighth, Wil Myers came off the bench and ripped a single to left field. He hit a pinch-hit homer on Saturday. It was further proof that the Padres have found a nice rotation among their four outfield options. 

Hunter Renfroe is getting regular starts, while Naylor, Myers and Manuel Margot share time somewhat evenly based on matchups. The outfield plan is coming to fruition.