"We battled and stayed right there," Jennings said. "Had a look at it in the ninth inning, bring the tying run to the plate, but unfortunately we just couldn't get that hit."
Miami lost 2 of 3 to Washington, but has seven games against them in September as well as six against the first-place Mets.
"It's a chance to play the spoiler," Jennings said. "It's a great experience for a lot of these young guys; and some of our young pitchers especially are getting opportunities to showcase their abilities. And for the most part they are stepping up in a big way."
Michael Taylor added two singles and scored twice for Washington, which got hits from all eight starting position players and remains 5 1-2 games behind the Mets in the NL East.
Strasburg was lifted with upper back discomfort after four innings. He gave up four runs on seven hits.
Papelbon picked up his 22nd save.
Miami starter Brad Hand (4-4) allowed five runs on eight hits over 4 2-3 innings.
Hand, who had won three of his last four starts, fell to 0-6 with a 7.96 ERA in 10 games versus Washington.
The Nationals pulled ahead in the fifth. Werth doubled home Taylor and scored on a single by Bryce Harper to tie it.
"I made a mistake to Werth for the double," Hand said. "But then after that I got two outs with Harper up with two strikes, and I just left the pitch over the plate a little too much and he hit it and I couldn't make another pitch after that."
Robinson's two-run blast in the sixth provided some cushion.
Strasburg had gone 3-1 with a 1.73 ERA in four starts since coming off the disabled list after missing more than a month with an oblique strain.
After giving up five earned runs in those four starts, he was touched for three in the first inning Sunday.
Gordon led off with a bunt single and went to third on Ichiro Suzuki's double. One out later, Bour homered to right-center for a 3-0 Marlins lead.
Washington got to Hand in the third when Taylor singled and Werth lined a 3-2 pitch into the Nationals bullpen to make it 3-2.
Dietrich homered into the second deck in right to open the fourth.
With his double Sunday, Suzuki has 2,924 Major League hits, all coming after he turned 27. He moved ahead of Sam Rice and now trails only Pete Rose (3,353) for most hits after reaching 27, according to STATS.
Marlins: OF Christian Yelich (bruised right knee) was out of the starting lineup for the fourth straight game, but singled as a pinch hitter in the ninth.
Marlins: LHP Chris Narveson (1-1, 7.04 ERA) makes his second start of the season when the Marlins begins a three-game series at Atlanta.