SAN FRANCISCO -- The last time the Giants faced Rockies right-hander German Marquez, they nearly found themselves on the wrong end of history.

Marquez fired his first career shutout in his last start in San Francisco on April 14, coming within four outs of no-hitting the Giants for the first time at Oracle Park. They enjoyed more success against Marquez on Wednesday, but they still fell short of clinching a series victory against the Rockies, falling, 6-3, in the rubber game of their three-game series.

Pablo Sandoval went 2-for-4 with a home run and two RBIs, but the Giants couldn’t overcome a rough start from right-hander Jeff Samardzija, who allowed an early two-run lead to slip away after surrendering a grand slam to David Dahl in the third inning.

“He’s having a pretty good year, and he got a pitch he could handle,” manager Bruce Bochy said of Dahl. “It ended up being the difference in the ballgame.”

• Box score

Here are three takeaways from the opening series of the Giants’ current seven-game homestand:

1) New look at the top of the lineup shows promise

The Giants’ first-inning woes have been well-documented this season. Entering Wednesday, they had been outscored by an absurd 75-19 margin in the opening frame, prompting Bochy to make some changes at the top of his lineup. On Tuesday, Bochy decided to slot first baseman Brandon Belt into the leadoff spot for only the second time in his career and give newcomer Alex Dickerson a look in the cleanup spot.

“I’m going to look at it for a little bit,” Bochy said. “It wasn’t a day thing. We’ll see how it goes.”

Belt led off Wednesday’s game with a groundout, but the Giants still managed to take a rare early lead against Marquez. Mike Yastrzemski reached on an error after Marquez fumbled a feed from first baseman Daniel Murphy, and Sandoval followed with an RBI double to center field to open the scoring. Dickerson then added another double to left, scoring Sandoval and extending the Giants’ lead to 2-0 in the first.

The Giants’ third run of the game came on Sandoval’s 10th home run of the season -- a 444-foot bomb to straightaway center field in the third -- but Bochy said he was encouraged by what he saw from atop the lineup and could stick with the same grouping of lefty bats against right-handed pitchers moving forward.

“We had some great at-bats,” Bochy said. “We hit a lot of balls hard. I thought it was one of our better days offensively, even though we only scored three. I thought we had some really good at-bats in the first five innings there. Hard contact, some hard outs mixed in there. We just couldn’t have a big inning like they did.”

2) Samardzija remains mired in a rough patch

Samardzija opened his start by retiring the first six batters he faced, but things quickly unraveled after he issued a leadoff walk to Tony Wolters in the third. Garrett Hampson followed with an infield single and Charlie Blackmon walked to load the bases with one out for Dahl, who drove a 3-2 fastball just over the left-center-field fence for a grand slam, putting the Rockies ahead, 4-2.

“Frustrating is a great way to put it,” Samardzija said. “I felt good out there. I think we hit all our spots. The ball was coming out well. It’s just walks. I’ve talked about it before. They always come back to haunt you.”

Colorado added another run in the fourth after Raimel Tapia led off the inning with a triple and scored on a sacrifice fly by Wolters. Samardzija departed after yielding five runs on three hits over five-plus innings, marking the fourth consecutive outing in which the 34-year-old veteran has allowed at least three runs. He’s allowed 17 runs over 21 1/3 innings (7.17 ERA) over that stretch, causing his ERA to spike to 4.52 on the season.

The main issue for Samardzija has been his tendency to succumb to big innings after suffering lapses in his command.

“Usually when you’re throwing up zeros and then crooked numbers, they’re getting hits or you’re walking guys when you’re in the stretch,” Samardzija said. “It’ll be something to address here going forward, and we will.”

3) Dickerson continues to impress

The last couple of weeks have been quite a whirlwind for Dickerson, who was acquired from the Padres in exchange for Minor League right-hander Franklin Van Gurp on June 16. Dickerson, 29, reported to Triple-A Sacramento before the Giants called him up Friday to replace the injured Steven Duggar.

He’s delivered a much-needed offensive boost in his first six games with the club, going 9-for-21 (.429) with four doubles, one triple, one homer and 10 RBIs. It’s a small sample size, but the Giants are hoping Dickerson will be able to continue to provide the type of power and production that’s been missing from their lineup for most of the season.

“Two weeks ago, I was waiting on my couch waiting to see if anyone wanted to grab me while I was on designation,” Dickerson said. “A week ago, I was in Sacramento. And then right when I felt like my swing was going to come around, I got the opportunity to come here. It’s played out well. I’m just trying to have fun with it.”