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Last week, Ross Detwiler helped the Washington Nationals franchise secure its first playoff spot since 1981.

On Tuesday, the southpaw looks to lower the club's magic number for claiming the NL East crown in the opener of a three-game series with the Philadelphia Phillies.

Detwiler has not lost in five straight starts, winning three decisions in that span. He is coming off Thursday's victory over the Los Angeles Dodgers that sealed up at least a wild card berth for the Nats. Detwiler allowed just a single run over six innings, scattering three hits and a walk while striking out five.

The 26-year-old moved to 10-6 with a 3.10 earned run average in 31 games this season, 25 of those starts.

Detwiler logged seven scoreless innings of three-hit ball the last time he faced the Phillies on Aug. 2, moving to 2-3 against them with a 3.57 ERA in seven games (6 starts).

Washington followed that set with Los Angeles by splitting a four-game series with the Milwaukee Brewers, winning Monday's finale by a 12-2 margin.

Ryan Zimmerman had three hits and four RBI, homering during a six-run fourth inning that also saw starter Jordan Zimmermann hit a two-out single that scored the first run of the big frame to snap a 1-1 tie.

On the mound, Zimmermann logged 6 2/3 innings, the only run he allowed coming on a solo homer in the second inning.

"I was throwing the fastball and getting ahead, and when I do that, I feel like I can control the game," Zimmermann said. "I'm glad I'm having a few good ones here as the regular season is coming to a close."

With the victory, the Nationals have a magic number of five to clinch the NL East as they lead the Atlanta Braves by five games. The Braves open a three- game series versus the visiting Miami Marlins on Tuesday.

The Nationals appear set to unseat the Phillies, who have won the past five division titles but saw their late-season charge at a postseason spot suffer a big blow with back-to-back losses to the Braves over the weekend.

Philadelphia dropped a 2-1 decision on Sunday, held to just two hits. It now trails the final playoff spot in the league by 5 1/2 games with nine to play.

One bright spot this season for the Phils has been Cole Hamels, who takes another shot at a career-high 16th victory of the season tonight.

Hamels, who also won 15 games in 2007, is 4-0 over his last eight outings and the Phillies are 7-1 in that time when he starts.

The lefty hasn't lost since a 3-0 decision to the Nationals on Aug. 2. Hamels allowed three runs -- two earned -- in seven innings while fanning nine. That left him 12-5 with a 2.48 ERA lifetime in this series.

Hamels did not get a decision on Wednesday versus the New York Mets despite striking out 10 over six innings of work. He yielded two runs on six hits and a walk in a game his club won 3-2.

The 28-year-old is 15-6 with a 3.05 ERA in 29 starts and is third in the NL with 202 strikeouts.

The Phillies swept a three-game set at home over the Nationals in the most recent encounter and have won six of the last seven in this series.