(Sports Network) - The Arizona Diamondbacks hope to break out of a recent rut when the National League West leaders open up a three-game series with the Washington Nationals tonight at Chase Field.

Arizona is presently mired in a season-high four-game losing streak and has dropped eight of its last 10 contests following Thursday's 4-3 home setback to San Francisco. Despite their slide, the Diamondbacks still own a comfortable 3 1/2-game lead on second-place Los Angeles in the NL West standings.

The lowly Giants completed a surprising three-game sweep with Thursday's triumph, in which San Francisco scored a run in both the eighth and ninth innings to overcome a 3-2 deficit.

Randy Winn delivered the go-ahead blow when he homered off Arizona reliever Chad Qualls (0-5) to lead off the top of the ninth. Winn also had a solo homer in the fourth against D-Backs starter Randy Johnson.

Johnson pitched well despite not factoring in the decision, as the legendary lefty held the Giants to two runs and recording nine strikeouts over seven innings. The 44-year-old's final strikeout of the night gave him 4,672 for his career, which tied Roger Clemens for second place on the all-time list.

Justin Upton went 2-for-4 with a two-run homer to pace Arizona offensively.

The Diamondbacks will attempt to get back on track tonight against Tim Redding, a pitcher the club has dominated in recent years. The Washington right-hander is 0-5 with a 6.30 earned run average in six career starts against Arizona, although he hasn't faced the D-Backs since the 2005 season.

Redding has been rock-solid so far for the Nats, as the veteran hurler leads the squad with six victories while posting a nice 3.59 ERA over 11 starts. He's also excelled on the road this year, having won all three of his away starts and allowing just five runs over a combined 19 innings of work.

The 30-year-old is not coming off one of his best efforts of the year, though. Against Milwaukee on Sunday, Redding was tagged for five runs and a season- high 10 hits over 5 2/3 innings and received a no-decision in a 7-6 Nationals' win.

Redding will be opposed tonight by Diamondbacks rising star Micah Owings. The second-year major leaguer has won six of eight decisions to start the season and surrendered three runs or less in eight of his 10 starts for the year.

Owings comes in off a winning effort at Atlanta on Sunday, with the 25-year- old permitting three runs -- two earned -- and six hits over six solid frames. Prior to that outing, Owings struck out a career-best 10 batters over seven innings in a 3-2 loss at Florida on May 20.

The young right-hander had two excellent starts against the Nationals as a rookie last season. Owings yielded just one hit over five scoreless innings to defeat Washington in his major league debut back on April 6, 2007, then delivered 6 1/3 innings of one-run ball during a no-decision at Chase Field last August.

Washington has lost three of its last four games and was handed a 5-2 defeat by San Diego on Thursday, with the Padres' Jody Gerut slugging a tie-breaking three-run homer off Nats reliever Charlie Manning in the bottom of the eighth inning.

Saul Rivera (3-3) took the loss for Washington after allowing two consecutive singles prior to Gerut's blast off Manning. John Lannan worked the first six innings and surrendered two runs on five hits while striking out five.

Arizona won six of seven encounters with Washington in 2007, but the Nationals went 5-1 against the Diamondbacks during the previous season.