Joc Pederson feels the power in Dodgers’ 6-2 win over the Diamondbacks

The television in the visiting manager’s office at Chase Field showed the final inning of Saturday’s second-most important game for Dave Roberts.

As San Francisco attempted to close out St. Louis, Roberts kept his eyes pinned on the reporters surrounding him as he discussed a 6-2 Dodgers victory over the Arizona Diamondbacks. The Giants always reside on his periphery, but rarely are his focus.

“We’re all looking at the scoreboard,” Roberts said. “But it’s a nice position for us to be in, to just control our own fate, and to win baseball games.”

A few minutes later, the San Francisco bullpen did what it has done so often in the second half. It collapsed, kicking away a lead and allowing the Dodgers to extend the lead in the National League West to five games.

As the Giants crumbled, the Dodgers replicated a version of their common formula for victory: Five decent innings from a starter, some power from their offense, an ability to capitalize on mistakes by their opponents.

Making the fifth start of his career, rookie Brock Stewart supplied five innings of two-run baseball. The Diamondbacks tagged him for a pair of solo home runs, but little else.

The offense benefited from Arizona’s consistently inept defense. Joc Pederson keyed a three-run fourth inning with a two-run homer. Chase Utley doubled twice. Josh Reddick recorded three hits. Corey Seager notched two hits, including a triple in the first inning, which gave him 181 hits on the season, the most by a Dodgers rookie since the team moved to Los Angeles.

With a win on Sunday, the Dodgers can finish this 10-game trip with more victories than defeats. After dropping two of three in Miami, the Dodgers won twice at Yankee Stadium and won two of the first three games this weekend in Arizona.

A three-game set with San Francisco starts at Dodger Stadium on Monday. The Dodgers have aligned their rotation in an attempt to remove all doubt. Clayton Kershaw will face Madison Bumgarner on Monday. Rich Hill draws Johnny Cueto on Tuesday. The series ends with Kenta Maeda dueling Matt Moore.

The Dodgers snatched a run in the first inning on Saturday. In the game’s second at-bat, Seager deposited a hit into right field, the domain of Yasmany Tomas, Arizona’s comically inept right fielder. The baseball bounced off the wall along the line. By the time Tomas had corralled it, Seager was heading to third base, and Arizona starter Shelby Miller was raising his arms in exasperation. Seager scored on a sacrifice fly by Justin Turner.

Stewart handed back the lead by allowing a solo shot to infielder Jean Segura in the bottom of the inning. But the Dodgers soon received a gift in the form of another defensive gaffe in the fourth. Adrian Gonzalez led off with a walk. Reddick dunked a single into right.

With Pederson at the plate, Arizona catcher Welington Castillo dropped a fastball and let it trickle behind him. Both runners broke for the next bag. Castillo secured the baseball in time to peg Gonzalez at third, but his throw landed in left field.

Gonzalez jogged across the plate and Reddick took third. Pederson only needed to produce a flyball to add another run. He provided much more. He fouled off a pair of curveballs as the count ran full. Miller tried to stuff a fastball past Pederson’s knees. Pederson unleashed hellacious power for his 23rd home run.

“I was just doing whatever I could to try to bring him in,” Pederson said. “It worked out well.”

Stewart ran into trouble in the bottom of the inning. He struck out the first two batters, but then he fed Castillo a 92-mph fastball at the belt. Castillo clobbered a homer deep into the seats in left.

The pressure continued to build. Tomas hit a single. Stewart walked outfielder Brandon Drury. The next batter, outfielder Mitch Haniger, hit a single into left. With two outs and the pitcher on deck, Arizona third base coach Matt Williams decided to send Tomas home.

The baseball skipped toward Andrew Toles. He set his feet and fired a strike to catcher Carlos Ruiz. The ball beat Tomas by several feet, and Ruiz applied the rally-ending tag.

“That little guy has got all kinds of fire, and stuff you don’t really expect out of him,” Reddick said. “And now he showcased an arm that can throw about 100 mph to throw a guy out by 10 feet. That was pretty impressive.”

The Dodgers kept extending the lead. Utley hit an RBI double in the seventh. Seager scored from third on a wild pitch in the ninth. A little while later, he joined the rest of his teammates to watch San Francisco collapse again.

“This is that fun time of the year,” Seager said. “You get done with your game, you come in and you watch theirs. It’s fun for us, it’s fun for the fans. It’s the point in the year that everybody looks forward to.”

andy.mccullough@latimes.com

Follow Andy McCullough on Twitter @McCulloughTimes