(My Sportsbook) - There's nothing like opening your Major League career in the heat of the playoff race. Just ask Washington Nationals righthander Darrell Rasner, who will be making his first career start against the Florida Marlins in the second of a huge four-game series at RFK Stadium.

With Tony Armas Jr. unable to take the mound due to on-going shoulder issues, the Nationals have had to turn to Rasner, who was called up from Double-A Harrisburg. Rasner registered a 6-7 mark with a 3.59 ERA at Harrisburg this season.

Florida will respond with veteran righthander Ismael Valdez on the hill. Valdez is 0-1 in his last five outings, including a no-decision versus St. Louis last Tuesday. The 32-year-old surrendered six hits and four runs over six innings, while fanning five and walking one. Valdez is 1-1 with a 5.50 ERA in four road outings this year.

Valdez has tallied a 6-5 record with a 3.43 ERA versus the Nationals/Expos in his career.

The Nationals grabbed the upper hand in this series on Monday, posting a 5-2 victory. Washington moved to within 1 1/2 games of Houston for the NL wild card, while Florida is one contest back.

Livan Hernandez went eight-plus innings to lead the Nationals to the win. Hernandez (15-6) scattered six hits and allowed two runs while striking out four in a clutch performance. He also went 2-for-4 at the plate and helped himself with an RBI.

Marlon Byrd drove in three runs to lead the Nationals' offensive attack. Byrd finished the day 3-for-5, including a double and a triple, while Deivi Cruz added a pair of hits.

Nationals infielder Jose Vidro (sore right knee) continues to be on the sideline. Vidro will likely be out for tonight's game.

Washington, which is in the middle of a huge 10-contest homestand, is 39-27 in its friendly confines.

Rookie Florida starter Jason Vargas (5-3) took the loss Monday despite a solid five-plus innings. He gave up a run on seven hits and struck out four.

Miguel Cabrera belted a two-run homer in the ninth to highlight Florida's offense. Luis Castillo posted a pair of hits in the contest.

Florida shortstop Alex Gonzalez is out with an inflamed elbow and will likely miss the next week of play. Damion Easley filled in for Gonzalez Monday, going 1-for-3.

The Marlins, who are in the early stages of an 11-game road trip, are 31-34 in foreign buildings this season.

These teams have split 14 meetings this season.