SAN DIEGO -- For an idea on just how relentless the National League West race has been this season, consider this:

Just as the Padres and Nationals were getting underway at Petco Park on Monday night, the Giants and Dodgers lost their games. If it felt like a rare opportunity for San Diego to gain ground on its primary divisional rivals, well, it was.

The last time the Giants and Dodgers lost on the same day was June 12 -- but even that wasn’t quite the same opportunity. The Giants played a doubleheader that day, and won the other game. It had been since June 6, nearly an entire month, that the Padres had been presented with an opportunity to gain a full game on both San Francisco and Los Angeles.

Opportunity squandered. The Padres rallied from an early five-run deficit, but still lost their series opener against the Nationals on Monday night, 7-5, at Petco Park.

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“You feel good once you tie it up,” said Padres manager Jayce Tingler. “You felt like we were going to be able to get some more runs on the board. And that just didn’t happen.”

No fault of Joe Musgrove’s. The right-hander kept the Padres in the game, even after falling victim to some seriously rough batted-ball luck in the second inning. By the time it was over, the Padres trailed 5-0, and Nick Ramirez was getting loose quickly in the home bullpen.

Musgrove resolved to keep his team in the game. In efficient fashion, he retired 11 of the final 12 hitters he faced and managed to grit through five innings -- which seemed like a near impossibility when his pitch count climbed to 56 by the end of the second.

“I’ve got no trouble fighting,” Musgrove said. “Especially with the offense that we have here, and the team that we have here, I don’t feel like I’m ever out of the game.”

He wasn’t. The Padres rallied for three in the second inning (and it could’ve been four had Ha-Seong Kim’s double found its way into the left-field corner rather than taking an unfortunate ricochet off a stool for the team’s ball girl).

San Diego tied it in the fourth. Fernando Tatis Jr.’s National League-leading 27th homer was a 116-mph missile off the Western Metal Supply Co. building -- the hardest-hit ball of Tatis’ career. Jake Cronenworth followed with a double and scored the tying run two batters later on Wil Myers’ double.

“It was good to get back in it,” Tingler said. “But frustrating, disappointing not to muster up really anything after the fifth.”

Further theatrics from Tatis weren’t enough. The Padres star shortstop defied gravity to make an absurd leaping catch in the top of the eighth inning. But the Nationals had already taken the lead in the seventh on Josh Bell’s go-ahead blast off Tim Hill and they tacked on another in the eighth.

And that was that. Presented with a rare opportunity to make up ground on both the Dodgers and the Giants, the Padres couldn’t do so.

There will, of course, be future opportunities. Across the season’s final six weeks, the Padres play those two teams a combined 19 times. Meanwhile, the Giants and Dodgers will play each other seven times in a 10-day stretch in late July.

Based on the records, they’re three of the four best teams in the National League, and there’s only one spot in the NL Division Series without the burden of a winner-take-all Wild Card Game. Those high stakes should make for some incredible theater down the stretch.

“This is what you want,” Musgrove said. “This is why you play the game. We want it to come down to the last month. The last month of the season, looking at the schedule, it’s pretty much all Dodgers and Giants. … If things can stay as tight as they are, it’s going to make for an exciting last month, and at that point, we’ll really see what teams are made of.”