WASHINGTON -- Over the course of three days in the nation’s capital, Marlins manager Don Mattingly was asked repeatedly about just how difficult it is to match up against the Nationals, the best team in the Majors since late May. No reminder of that challenge was really needed, given Washington’s stretch of 12 wins in the past 13 head-to-head meetings.

There was no reminder needed, but the Marlins got one anyway, suffering a sweep-clinching 9-3 defeat to the Nationals on Sunday at Nationals Park that extended the club-record road losing streak to 15 games.

• Box score

“Certain teams let you know where you are at,” Mattingly said, “and these guys are one of those teams.”

True, no team enjoys being swept. The Marlins were definitely among that group come late Sunday afternoon, when they boarded a flight to Pittsburgh, where they will try to end their road woes starting Tuesday.

Equally true is the notion that lessons for a young team don’t need to come amid the disappointing circumstances of a sweep. But if there is anything positive to hold onto from a frustrating series in D.C., it’s that there are, at least, some of those lessons to soak up.

“To be able to get to the next step, you have to be able to beat this team,” said Miguel Rojas, who went 0-for-4 with a fielding error in his first start off the injured list. “By this sweep, we are going to learn a lot and we are going to move forward, but we have to start playing better baseball.”

Rojas spent his time on the mend making sure to catch his teammates on TV as they fought through a tough August. As he continues to nurse his right hamstring, which he said is not quite 100 percent, his first start back did not provide much in the way of aid. But the worries do not end at him.

The Marlins allowed 23 runs and eight homers (with all the homers coming in the series' final two games) while striking out 36 times themselves against the Nationals’ vaunted pitching staff. But they were in fact close in two games. Starlin Castro's go-ahead homer in the ninth on Friday was eventually erased, and Caleb Smith rivaled Patrick Corbin’s early-inning dominance before his Sunday afternoon got out of hand in the sixth inning.

“You have to tip your cap to them, too,” Rojas said, “but we have to play better baseball.”

The Marlins’ best chance at a win came when they chased Anibal Sanchez from Friday’s game early. Unlucky for them, their next two opportunities against National League Cy Young Award candidates Stephen Strasburg and Corbin provided little room for reprieve.

The box scores reflected that concern. Miami mustered just six hits in the series’ final two contests.

“I don't know, honestly, at this point, what we are gaining from getting swept,” Mattingly said. “Hopefully we are gaining information. Good or bad, you see success -- or lack of success -- against not just a team but certain pitchers, guys that are atop the totem pole, what our guys look like.”

Smith was chief among that grouping on Sunday. An error allowing the first Nationals run to score was the only Miami blemish in the early going. Both Mattingly and Smith thought he looked especially crisp to that point.

It wasn’t until three innings later, when Smith didn’t get a called third strike and then hit Victor Robles with the next pitch, that the homers finally started to bite him.

With the calendar flipped to September and baseball’s days running thin, all that’s left for him to do is what’s left for the team as a whole.

“Trying to finish strong,” said Smith, who gave up seven runs (six earned) over 5 1/3 innings. “Trying to go out and give my team the best opportunity to win. It’s just not working out right now.”