SAN DIEGO -- The Padres opened their final homestand of the regular season before another packed house at Petco Park on Monday night. Then they took a major step toward ensuring these six games won’t be the last games in downtown San Diego this year.

With a 3-1 victory over the Astros, San Diego moved closer to securing a spot in the postseason -- and padded its lead for the National League’s top Wild Card spot (which would ensure October baseball at Petco Park).

The Dodgers won in Atlanta on Monday, holding the Padres’ deficit in the NL West race at 3 1/2 games. But San Diego gained ground in the two other races worth monitoring.

With the Braves’ loss, the Padres own a 4 1/2-game edge on Atlanta, the first team on the outside of the playoff picture. Meantime, the Diamondbacks were walked off in Colorado, giving the Padres a 2 1/2-game edge on Arizona for the top Wild Card spot. That, of course, would come with home-field advantage in the Wild Card Series.

“Yeah, we’re right there,” said center fielder Jackson Merrill, who launched the 24th home run of his remarkable rookie season on Monday night. “But keep the head down and keep going.”

Added Jurickson Profar: “When you’re winning, you have a lot of fun. The way that we are doing it -- it’s more fun. Everyone is doing their part.”

Yu Darvish pitched six scoreless innings, allowing only three hits as he made a strong case for his inclusion in a potential Wild Card Series rotation. (It’s a testament to the current state of the rotation that the Padres have so many worthy options.)

Darvish missed three months while on the injured list and the restricted list. But Monday’s outing was his best start since his return in early September. Darvish kept Houston hitters off-balance all game and exited after six innings to an ovation and a chorus of “Yuuuuuu” from the Petco Park crowd. Manager Mike Shildt called the performance “vintage.”

“I’m super happy,” said Darvish, through interpreter Shingo Horie. “Our clubhouse, I think we’re really bonded together nicely, and we get to play in front of these fans. Obviously, the games are more exciting now. So it’s just super fun.”

Offensively, Luis Arraez bounced back from his first strikeout in 141 plate appearances with two hits, though he jammed his right knee after he was thrown out at the plate in the fifth inning. Arraez remained in the game and doubled in the seventh, but was clearly still affected and was substituted for a pinch-runner.

Arraez later said he hoped to be in Tuesday’s starting lineup but that he’d need to wait and see. Asked how he was feeling in the moment, he grinned.

“Mad,” said Arraez, whose streak without a K was the longest in the past 20 seasons. “I struck out.”

Still, Arraez’s two hits were part of a 13-hit night for the Padres. Profar had four, including an insurance homer in the eighth, and Merrill’s home run moved him two shy of Hunter Renfroe’s franchise rookie record (26).

With a two-run lead in the ninth, Shildt handed the ball to Robert Suarez in a save situation -- as he said he would, even after Suarez’s second blown save in three appearances on Sunday. Suarez nailed down a fourth Padres victory in four days.

In that span, the Dodgers, Mets and Braves have all lost twice. The Diamondbacks have lost three times. The Padres have gained significant ground on each -- and they’ve shifted their focus in the process.

They’re now closer to the top of the division than the cut line. Over the past few days, they’ve made it clear that chasing down the Dodgers in the NL West race remains a priority. Of course, the first priority is securing a spot in the postseason, and the earliest potential clinch date is Friday.

“I think there’s not too much focus on the big goal,” Merrill said. “When you’re really focused on having fun, playing the game, the big goal will come on its own.”

That’s precisely what the Padres have done, as they’ve posted the best record in the Majors since the All-Star break. They’ve made a point to maintain focus on the little things, saying the big things would take care of themselves.

“Everybody knows we have a really good team, especially right now,” Arraez said. “We compete, man. We have everything to win. We just need to stay healthy.”