Jeremy Hellickson couldn’t pitch the Nationals to a series win Sunday in Miami. (Jasen Vinlove/USA Today Sports)

Nobody with the Washington Nationals was willing to publicly acknowledge this weekend’s outsize importance to their season, but it was impossible to discount. They understood a poor showing against the rebuilding Miami Marlins could impact the franchise’s direction for the rest of this season and beyond with Tuesday’s nonwaiver trade deadline approaching. Play poorly and perhaps the front office will sell off pieces. Play well and maybe it will buy or at least stand pat and ride it out with the roster with which the team expected to contend for a World Series.

What exactly constituted a poor enough or a good enough showing was fuzzy, but their inexplicably lifeless, 5-0 loss at Marlins Park on Sunday in their final game before the trade deadline left them with a four-game series split, which tilts toward poor for the stupefied third-place team.

“Today’s game was just flat,” Nationals Manager Dave Martinez said.

The result dropped the Nationals one game under .500 at 52-53 with 57 games remaining. It’s the latest in a season they have been under .500 since August 2015 — the last time the club didn’t advance to the postseason. The Nationals traveled back to Washington six games behind the first-place Philadelphia Phillies and 4½ games behind the second-place Atlanta Braves. Their next game is Tuesday night against the last-place New York Mets, three hours after the trade deadline passes. The front office has decisions to make before then.

“I hate to put it in their hands,” Nationals outfielder Adam Eaton said. “If we do our job and come out and play, we put it in our own hands. . . . If we come out with a sense of urgency, we can do that. . . . We need to win three out of four from that team or take all four if we can. Same thing with Milwaukee [in the previous series]. I don’t know. I’m at a loss for words right now.”

Jeremy Hellickson drew the starting assignment Sunday and cruised through a 10-pitch first inning before succumbing to problems with two outs in the second.

The trouble began with Miguel Rojas dropping a blooper into shallow center field. Magneuris Sierra, the Marlins’ No. 8 hitter, then executed a hit-and-run to perfection, smacking a groundball up the middle to move Rojas to third base. That left the inning up to José Ureña, the pitcher. Ureña entered the day 1 for 30 with 22 strikeouts on the season. Ureña delivered the Marlins’ third straight two-out single, which scored Rojas and gave Miami a 1-0 lead.

The Marlins (46-61) added a second run with two outs the next inning when Martín Prado crushed a double over Bryce Harper’s head in center field. The hit drove in Brian Anderson, who was hit by a pitch to lead off the inning. A third two-out RBI hit chased Hellickson in the fifth. Prado delivered that one, too — a single to right field that scored Anderson again. As has been the case all season, Hellickson couldn’t survive facing a lineup a third time. He departed having thrown 81 pitches.

“Just got to bear down with two outs and get that last guy,” Hellickson said. “It’s happened too many games in a row now.”

The Nationals’ bleeding didn’t stop with Hellickson’s parting. Matt Grace replaced Hellickson and promptly induced a groundball that should have ended the inning. Instead Daniel Murphy misplayed it, and a run scored. Rojas then smacked an RBI double to make it 5-0. All five runs were charged to Hellickson, though only three were earned.

“I get a groundball to end the inning, I misplay it, and three turns into five,” Murphy said. “And it shouldn’t happen. When it goes from three to five, it puts a ton of pressure on the offense.”

While Hellickson relies on command, not overpowering stuff, to navigate through lineups, his counterpart Sunday takes the opposite approach. Ureña’s fastball sits in the mid- to upper-90s. His secondary stuff can be nasty. The problem is he often doesn’t know where it’s all going. The first four innings Sunday were a perfect case study.

Ureña walked four batters and hit another with a pitch before the fifth. The only Nationals hit to that point was an infield single by Harper. Washington hit the ball to the outfield twice. Ureña’s wildness was beyond effective. It was stumping the Nationals. Then Ureña delivered two perfect innings to complete his scoreless six-inning effort.

Washington didn’t fare any better against a meager Marlins bullpen that the Nationals have regularly destroyed this season. Adam Conley, Brad Ziegler and Drew Steckenrider combined to allow a hit and issue a walk — both in the ninth — over the final three innings. The Nationals went down with a whimper and perhaps for the final time before significant alterations are made to an underachieving roster.

“We shouldn’t have one hit going into the ninth inning against that team,” Eaton said. “That’s no offense to them. I just think with the quality of hitters that we have in this lineup and the way we go about our business. . . .

“We need a sense of urgency. It’s got to be now. Every single series from here on out should be a playoff series where we’ve got to win it. We’ve got to win every series. It’s got to happen now. It can’t happen next week. It can’t happen the week after. It’s got to happen now.”