WASHINGTON -- Matt Adams homered twice and collected seven RBIs, including a grand slam launched 438 feet into center field in the eighth, to help power the Nationals to a 15-5 victory in Sunday’s series finale against the D-backs.

Washington matched a season high with 15 runs to salvage a four-game split ahead of what will be one of the most important stretches of the season. Both Philadelphia and Atlanta are coming to Nationals Park for seven games this week beginning with a four-game series against the Phillies on Monday.

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“For me, this is a big week,” manager Dave Martinez said prior to Sunday’s game. “We got a chance to make up some ground here.”

“We’ve got to win those games,” said right fielder Adam Eaton, who reached base five times Sunday. “It’s important. We’re trying to chase at this point. Not to put too much emphasis on it, but we need to play some really competitive baseball.”

“Having two division rivals coming in, we got to protect our home turf and keep playing the baseball that we’ve been playing,” Adams said.

Those comments represent a break from the norm for the Nationals and Martinez -- normally fond of cliches about focusing on the moment or going 1-0 each day -- to acknowledge the magnitude of the week ahead. Even with Sunday’s win, the Nationals remain in fourth place and 8 1/2 games back of the first-place Braves in the National League East, but this is a direct opportunity to cut into that deficit.

“Obviously we all know who we're playing,” Martinez said. “They're ahead of us and we just got to worry about tomorrow. Keep playing like we're playing.”

It’s true, the Nationals have been playing much better baseball lately.

They have not lost a series since they were swept by the Mets on May 23 in New York. They have won 14 of 21 games since that point, thanks to a relentless offense capable of outbursts like Sunday, continued excellence from their starting staff and a much improved effort from the bullpen. Washington welcomes both teams into D.C. at a time where the Nats are healthiest and playing as well as they have all season, and they still have a ton of games left against both Atlanta (15 games) and Philadelphia (11 games).

“I think everything’s clicking right now,” said Adams, who homered twice with his father, Jamie, in attendance for Father’s Day. “We’re getting great pitching both from starters and the bullpen, and putting some runs across the plate.”

So now comes the test to see how legitimate this turnaround can be for a team clinging onto its postseason hopes.

The Nationals have been climbing uphill basically all season, not only because of their slow start to the year, but because of their continued trouble in series openers. Washington has dropped the first game in 17 of its 23 series, a trend that has often found the Nats trying to save face by the end of the series.

It’s something the Nats want to avoid in a week that could be make or break. A winning record this week could help convince the Nationals of their status as playoff contenders. A losing or even middling week makes that a much harder case to argue and could make Washington confront some difficult decisions ahead of next month’s Trade Deadline.

“And we shouldn’t beat ourselves these next four games,” Eaton said. “Play good baseball and not beat ourselves. If we play the brand of baseball we know how to play, and play clean, we have a good chance.”