"They wouldn't be here with the stuff they had if they didn't have confidence in it," shortstop Stephen Drew said of the Nats' pitchers. "They pitched well, and we didn't swing the bat well."
The team's frustrations were as evident as its struggles.
Trailing by four runs in the top of the seventh inning, the D-backs loaded the bases only to have Ryan Roberts strike out swinging to end the frame. After flailing at the offering from Jorge Sosa, Roberts spiked his bat in aggravation.
The D-backs did not have many opportunities to score. In the fifth, Alex Romero and Chris Young hit into scoring position only to have Martin snuff out the potential rally by recording three consecutive outs.
"Coming in on a high note [winning five straight before this series], we were swinging the bats pretty well," manager A.J. Hinch said. "Even in Game 1, we had a five-run inning in the second. From that point on, we never really delivered a ton of blows. It never really seemed like we could piece [hits] together or come up with a key hit at the same time."
The absence of No. 3 hitter Justin Upton, who is on the 15-day disabled list with a right oblique strain, has proved to be more costly than expected.
Serving as a replacement on Sunday, Trent Oeltjen deposited the third pitch of the game over the right-field wall, but the D-backs were held scoreless from then until the eighth, when Mark Reynolds homered for the fourth consecutive game. But it was a solo shot, and it only closed the gap to three runs.
Petit (2-6) followed a pair of stellar outings with an unremarkable one on Sunday. He gave up nine hits and four runs (three earned) in four innings before being pulled for a pinch-hitter.
"I struggled with command," Petit said. "I was leaving the ball up at the plate, and they hit it. My command on both sides was not working good."
Given an immediate lead thanks to Oeltjen, Petit handed it right back, allowing a two-run homer by Adam Dunn in the bottom of the first.
In the third, Ryan Zimmerman knocked his second double, and scored on Elijah Dukes' shot off Reynolds' glove with two outs. The next inning, Reynolds made a two-out throwing error to first, allowing Nyjer Morgan to score from second on an infield single.
Already leading by three, the Nationals added four insurance runs while batting around in the bottom of the eighth.
"Plain and simple, we got beat this series, and they outplayed us," said Hinch.