Joe Saunders looks to continue his impressive start and help the Diamondbacks win a fourth straight game Wednesday night against the slumping Nationals.After recording a 5.93 April ERA a year ago, Saunders (2-1, 0.90 ERA) has been lights out through the first month of this season for Arizona (13-11). The left-hander is limiting opponents to a .186 batting average, has 0.87 WHIP and has gone at least seven innings in each of his four starts.He is coming off one of the best outings of his career, tossing a three-hitter in Friday's 5-0 win in Miami."He's been great, very consistent," Kirk Gibson said. "He's taken the ball every fifth day and is really dominant with his stuff."Saunders has been at his best in his two outings away from Arizona, having yet to allow a run while yielding seven hits and four walks over 16 innings. He is 9-3 with a 2.30 ERA over his last 14 road starts, but one of his worst outings in this stretch came at Nationals Park.In the nation's capital on Aug. 22, Saunders gave up four runs in six innings of a 4-1 loss. He has a 6.00 ERA in losing his two career starts at Washington.The Nationals (14-9) were hoping a return home would help them get back on track after ending their road trip with a thud, but they dropped Tuesday's opener 5-1 extending their losing streak to five. They had only lost four times in their first 18 games.A punchless offense has been the biggest reason for this slump, as Washington has plated seven runs while batting .155 in its last five."I feel like we've got the hitters that can hit," manager Davey Johnson said. "Not as aggressive as I'd like to see. We're not getting a good strike and driving it. I know that talent is there. ... It's going to put a strain on the pitching staff if we don't start scoring some runs."The Nationals recalled Bryce Harper from the minors over the weekend to provide a spark, but he went 0 for 3 with a strikeout in his home debut Tuesday. Batting in the No. 7 spot in the order in his first three games, the No. 1 pick of the 2010 draft is 2 for 9.It's not going to get any easier for Harper against Saunders, whom left-handed hitters are 4 for 24 (.167) against with no extra-base hits and no walks.Arizona's offense could also have trouble against the Nationals, who have a major league-best 2.40 ERA and are tied with the New York Yankees and Los Angeles Dodgers for the most strikeouts with 202.Scheduled starter Edwin Jackson (1-1, 3.16) might be the weakest link in a superb rotation, but he enters May having thrown 10 2/3 scoreless innings over his final two April outings.Against San Diego on Thursday, Jackson allowed six hits and three walks in 6 2/3 shutout innings, but the Padres rallied to hand the Nationals a 2-1 loss. Washington has lost three of his four starts.The right-hander, who threw a no-hitter with Arizona in 2010, is 1-2 with a 3.33 ERA in four career starts against his former team, and he'll have to be careful pitching to Jason Kubel and Justin Upton.Kubel is batting .467 with two home runs, four doubles and seven RBIs in his last seven games, and is 2 for 8 with a homer and double against Jackson since 2009.Upton, who had two hits and two RBIs Tuesday, has singled in all three of his at-bats against Jackson.