Joe Saunders leads the major leagues with a 0.90 earned run average and the Arizona Diamondbacks hope he can keep it that way tonight in the second test of a three-game series against the Washington Nationals.

Saunders is 2-1 in four starts so far this season and is coming off the first shutout of the season and third of his career in a 5-0 win at Miami on Friday. He held the Marlins to just three hits, struck out four and issued a pair of walks, lowering his ERA from 1.29 to its current state.

The left-hander has yielded just three earned runs all seasons and is set to take on Washington for the fifth time in his career. Saunders is 2-2 over the initial four starts with a 2.89 ERA.

D'Backs starter Trevor Cahill did his job in last night's series opener by holding the NL East-leading Nationals to a run on six hits and one walk over 7 1/3 innings of a 5-1 victory. He struck out five batters to even his record at 2-2 this season.

"He kept the ball down today, a lot of action on his ball, a lot of late life," Diamondbacks manager Kirk Gibson said of Cahill. "He stayed in control of the game."

Bryan Shaw and David Hernandez kept Washington off the boards the rest of the way. As for the offense, Justin Upton had two hits and two RBI, while Miguel Montero and John McDonald finished with two hits and an RBI apiece. Paul Goldschmidt had three hits and scored a run for Arizona, which has won three in a row and six of nine games. Aaron Hill has reached base safely in 18 straight games.

The Diamondbacks are 4-1 on a 10-game road trip and 7-4 outside of the desert.

Washington is mired in a season-high five-game losing streak after it had won four straight and seven of eight games. In last night's loss at Nationals Park, Jordan Zimmermann started on the hill and allowed four runs, three of which were earned, and eight hits in 6 1/3 frames.

Ian Desmond had two hits and knocked in the lone run, and Steve Lombardozzi finished 2-for-4. The Nationals have scored just seven runs during their current losing streak.

"That's just not going to cut it," Nats manager Davey Johnson said. "You go through spells, but you've got to have a lot of confidence in the talent and keep looking for us to break out. Tomorrow's another day."

Tuesday also marked the home debut for Nationals outfielder Bryce Harper. The first overall draft pick in 2010, Harper received a standing ovation prior to his first home at-bat, in which he struck out in the second inning. He finished 0-for-3.

The Nationals, who sit just one-half game ahead of Atlanta in the division standings, will also welcome Philadelphia to town on their six-game residency and are 8-3 in D.C. this season.

Toeing the rubber for Washington tonight will be Edwin Jackson, who is 1-1 with a 3.16 ERA through the first four starts with his new club. Jackson did not record a decision in Thursday's 2-1 loss at San Diego despite throwing 6 2/3 shutout innings and yielding six hits.

Jackson fanned six Padres and walked three, and has at least five K's in each start this season. The right-hander and former Diamondback from 2010 is 1-2 with a 3.42 ERA in five career games (4 starts) against Arizona. Jackson went 6-10 with a 5.16 ERA in 21 starts with the D'Backs a few years ago. He threw a no-hitter on June 25th, 2010.

The Diamondbacks and Nationals are meeting for the first time this season, and Arizona won five of the eight encounters a year ago. The D'Backs are unbeaten in the previous four matchups.