Washington salvaged the final game of the three-game set to earn its first victory since clinching the NL East on Sunday.
In his second career start, Robles, who entered the year as the top prospect in the Nationals' organization and made his major league debut last week, offered a few more glimpses of his coveted skillset.
The 20-year-old tripled right-center in the fourth off Atlanta starter Mike Foltynewicz (10-13), showing no interest in settling for a double as he zipped around second. He scored two batters later on Pedro Severino's fielder's choice grounder to make it 3-0.
Roark (13-9) at one point set down 12 in a row and did not yield a hit until Johan Camargo's two-out single in the fifth. He struck out seven over six innings, giving up four hits and two runs.
Sean Doolittle pitched the ninth for his 18th save in as many opportunities since Washington acquired him in a trade from Oakland in July.
