By JEFF BARTL
(AP) -- The Washington Nationals' starting rotation is among the best in baseball, but not even the addition of phenom Bryce Harper has been able to spark their sputtering offense.
Harper will make his home debut as the Nationals look to avoid a fifth consecutive loss Tuesday night in the opener of a three-game set with the Arizona Diamondbacks.
Washington's starters lead the majors with a stellar 1.78 ERA while holding opponents to a .186 average. Gio Gonzalez allowed two runs and three hits in six innings Sunday, but didn't get any support in a 2-0 loss to the Los Angeles Dodgers - the team's fourth straight defeat.
The Nationals (14-8) rank near the bottom of the league in providing 3.23 runs per nine innings for their starting pitchers, and they've totaled six runs during their skid.
The 19-year-old Harper has gone 1 for 3 in each of his first two major league games, driving in a run in Saturday's 4-3, 10-inning loss.
"It's frustrating for our pitching," first baseman Adam LaRoche told the team's official website. "We feel terrible, because they are doing everything they can possibly do. They are throwing some great games - all of them. We are not pushing the runs across."
Jordan Zimmermann (1-1, 1.33 ERA) was on the mound for the team's last victory, earning a 7-2 win Wednesday at San Diego after allowing one run in six innings.
He's given up one earned run in each of his four starts and was provided with welcome run support in his last outing after receiving a combined two runs over his first three starts.
It was a similar story for the right-hander in his most recent start against Arizona, a 2-0 home loss Aug. 23. Zimmermann gave up one run in seven innings to beat the Diamondbacks 6-1 on June 2 in his only other outing against them.
Harper, who heard some boos in Los Angeles, should get a warm welcome in his first major league home game. Washington is 8-2 at Nationals Park behind a 1.52 ERA from its starters.
Harper made a highlight-reel catch Sunday after starting in center field in the absence of Jayson Werth, who was a late scratch with a migraine headache. Tyler Moore, another highly regarded prospect, made his major league debut in left field and went 1 for 3.
Werth, who is hitting .382 with eight homers in his last 15 games versus Arizona, likely will be back in the lineup Tuesday when the Diamondbacks send Trevor Cahill (1-2, 3.70) to the mound.
Cahill has struggled in his last two starts. He allowed seven runs - four earned - in 5 2-3 innings of a 9-1 loss to Atlanta on April 20, then gave up four runs in 5 1-3 innings in a 7-2 loss to Philadelphia on Wednesday.
The right-hander, who has never faced the Nationals, is 1-0 with a 1.35 ERA in his two road starts.
Arizona (12-11) began its 10-game trip by taking three of four in Miami, capped by a 9-5 victory Monday as Justin Upton and Cody Ransom each hit a two-run homer. Diamondbacks starters had a 1.32 ERA in the series.
"Overall I think we have been playing great," manager Kirk Gibson said. "Guys are loose and enthusiastic to play the game."
The Diamondbacks won three of four in their last visit to Washington from Aug. 22-25.
Updated April 30, 2012