Ross (2-1), making his third career start, surrendered just one run and five hits with 11 strikeouts. He also recorded his first career hit.
Wilson Ramos finished with two hits and two RBI and Yunel Escobar and Danny Espinosa each drove in a run for the Nationals, who ended a four-game home losing streak despite not having star outfielder Bryce Harper in the lineup due to a strained left hamstring.
Gregory Polanco's RBI single accounted for the Pirates' lone run and A.J. Burnett (6-3) was rocked for four runs -- three earned -- and 14 hits with seven strikeouts over 6 2/3 frames.
Denard Span and Anthony Rendon each singled to open the home first and Span hustled home on Escobar's groundout. Two batters later, Ramos hit an RBI double for an early 2-0 Washington lead.
In the second, Jung Ho Kang led off with a single and moved to third on Francisco Cervelli's base hit to right field. Polanco followed by cutting the deficit in half with a run-scoring single.
With the bases loaded and one out in the home half, Burnett escaped a jam by inducing an inning-ending double play off a Rendon grounder.
Escobar added to the Nationals' lead in the third by opening the frame with a base hit, moving to second on a throwing error, taking third on a line out and scoring on Ramos' base hit to center for a 3-1 score.
Meanwhile, Ross fanned Andrew McCutchen to end the third and struck out the side in the fourth.
Tyler Moore doubled to open the fifth and Ross registered his first career hit with a one-out single. Rendon walked two batters later to load the bases with two outs, but Escobar grounded out to leave them stranded.
Espinosa hit an RBI triple off the wall in right past a leaping Polanco for a 4-1 advantage with two outs in the seventh. Polanco left the game with an injury and was replaced by Jose Tabata.
David Carpenter relieved Ross and recorded the final two outs in the eighth and Drew Storen struck out two in a perfect ninth for his 20th save of the season.
Washington won its fifth straight game against Pittsburgh ... Ramos has reached base safely in each of his 21 career games against the Pirates ... Burnett surpassed Andy Pettitte for 37th on the all-time strikeout list with 2,451 ... Pirates second baseman Josh Harrison extended his hitting streak to nine games ... Prior to the game, the Nationals placed pitcher Tanner Roark on the paternity list and recalled pitcher Taylor Hill from Triple-A Syracuse.