The Arizona Diamondbacks are out to prove that first-place tag in the National League West is no joke.

Tonight, though, the Diamondbacks are faced with a tough challenge in the opener of a 10-game road trip with the first of three straight games against Roy Halladay and the Philadelphia Phillies at Citizens Bank Park.

Arizona has won six in a row and owns a 2 1/2-game lead over the struggling San Francisco Giants in the NL West. It polished off a three-game sweep of the New York Mets at Chase Field with a 5-3 victory on Sunday, as Justin Upton homered and Paul Goldshmidt finished 3-for-4 with an RBI and a run scored. Henry Blanco added two hits and two runs batted in for Arizona, which completed a 10-game residency with a 7-3 mark and now heads east.

"It's easy to say that this is going to be a big road trip," D'Backs center fielder Chris Young said. "But I think every game throughout the rest of the season is a big game. ... That's what we live for, and it's going to be a lot of fun."

Sunday's game wasn't fun for everyone. Diamondbacks new starter Jason Marquis sustained a fractured right fibula when he was hit by a comebacker off the bat of Angel Pagan in the third inning. Marquis was acquired from Washington before the trade deadline and is expected to miss 4-to-6 weeks. Micah Owings, Zach Duke or a Minor League prospect could take his spot in the rotation.

Duke got the win on Sunday even though he gave up two runs in 2 2/3 innings of relief. Owings tossed a scoreless inning and David Hernandez notched his 11th save in the ninth inning. Arizona won seven in a row from May 24-30 this season.

The Diamondbacks, who will also visit Atlanta and Washington on the trip, hope rookie Josh Collmenter can resume his solid play when he takes the mound tonight. He is 3-2 in his last five starts and ended a two-game slide in Wednesday's 6-3 victory over Houston. The righty held the struggling Astros to a pair of runs over seven innings with five K's and one walk.

Collmenter is 7-7 with a 3.51 ERA in 23 games (16 starts) this season and tossed a scoreless inning of relief in an 8-4 loss versus Philadelphia on April 27 at Chase Field.

Philadelphia had an extra day of rest after its series finale with Washington was postponed Sunday due to heavy rain. The game will be made up as a doubleheader on Sept. 20 at Citizens Bank Park.

The National League East-leading Phillies have won 13 of their last 15 games and split a pair of matchups with the Nationals. After losing Friday's series opener, 4-2, the Phils returned the favor with an 11-3 drubbing Saturday night behind seven strong innings from Roy Oswalt. Oswalt allowed three runs and six hits with five K's and one walk, while Michael Stutes worked the final two frames.

"Any time you get a little bit of help (on offense), you're able to be more aggressive," said Oswalt. "I was able to get the first pitch over and make them start swinging early."

Oswalt was referring to the help provided by Ryan Howard, who homered and drove in four runs. Raul Ibanez ended with two RBI and Jimmy Rollins scored three times for Philadelphia, which is a commanding 8 1/2 games ahead of Atlanta in the division and owns the best record in baseball at 78-41.

The Phillies are 21-8 versus teams from the NL West and will hand the ball to reigning NL Cy Young Award winner Halladay on Tuesday. Halladay is trying to become the NL's first 16-game winner and is aiming to reach that mark for the sixth consecutive year. The right-hander has won four straight starts and pushed his record to 15-4 in 24 trips to the hill in last Monday's 5-3 win at Dodger Stadium. He held Los Angeles to one run over 6 1/3 innings to lower his ERA to 2.51.

Halladay hasn't lost at home since April 19 versus Milwaukee and owns an 8-1 mark and a 2.26 earned run average in 13 starts in south Philly. He has faced Arizona three times in his career, going 3-0 with a 2.61 ERA.

Arizona took two of three matchups with Philadelphia from April 25-27 in the desert, but the Phillies are 10-5 in the past 15 meetings between the teams.