WASHINGTON -- In keeping with the norms of their long-simmering rivalry, Saturday's clash between D.C. United and the Chicago Fire at RFK Stadium offers plenty of intrigue for a mid-June league match.The two squads share top spot in the Major League Soccer scoring charts with 20 goals each. The hosts own an undefeated home record, while the visitors have yet to taste defeat on the road. And Saturday's winner, should the match provide one -- far from guaranteed, given that these clubs have racked up 13 draws between them -- will stand alone atop the Eastern Conference standings."It's going to be a great game, the No. 1 and 2 in the Eastern Conference," said D.C. defender Bryan Namoff on Friday. "It's always been a difficult match -- I think throughout the years it's been mounting into a definite rivalry, us and Chicago. So we're looking forward to it."As if there weren't already ample sources of motivation for a showdown with one of their least favorite adversaries, this week Namoff and his mates have spent time poring over their previous meeting with the Fire, a 1-1 draw in United's home opener on March 28. That night the Black-and-Red saw a dominating first-half performance canceled out by some slipshod defending on Patrick Nyarko's equalizer in the 53rd minute, leading to a frustrating result that D.C. considered two points lost.United believe they've made significant improvements in all departments during the intervening months, most of all in the defensive end, where they've allowed just two goals in their last three league matches. Continued vigilance will certainly be required against a Chicago attack that boasts more weapons than head coach Denis Hamlett can shoehorn into his starting XI."They actually have been fortunate on the road, having some success, especially when they came to RFK earlier in the season," said Namoff. "We actually had an opportunity to look back at that game a little bit, kind of went and talked about how we've progressed from that game until now, especially in the areas where they're going to be pretty strong in the attack, playing through Brian McBride."The spearhead of the Fire frontline, McBride has been a constant in the lineup all season, whereas Hamlett must decide if playmaker Cuauhtemoc Blanco is ready to start at RFK after the Mexican legend logged a full 90 minutes for his country in El Tri's 2-1 World Cup qualifying win against Trinidad and Tobago at midweek. The versatile Chris Rolfe has staked a claim to increased playing time in recent weeks and offers a speedier, more athletic alternative in Blanco's place.D.C. boss Tom Soehn also faces an ongoing selection conundrum thanks to his side's stacked frontline, though Luciano Emilio's red-card suspension will simplify matters on Saturday. Nevertheless, the adaptability shown by the likes of Chris Pontius, Santino Quaranta and Jaime Moreno makes United's shape and positioning unpredictable from week to week -- and even from minute to minute, as Soehn has displayed a penchant for tactical tweaks as the season has progressed."I think he's done a good job with that," said midfielder Ben Olsen this week. "He's got a good luxury with a lot of our players: Chris and Santino and Fred, Christian [Gomez] and Jaime, even -- those are all kind of interchangeable pieces. So if we need a little more defense and Pontius is playing forward, he can feel free to drop him back and if Tino's tired he can go up high. If we need something out wide that he sees, maybe they've got a weaker left back, maybe he'll put Fred out there to abuse him a little bit."Fire-United matches tend to be intense, ill-tempered affairs and with that in mind, Soehn gave his charges a rare weekend off after last Thursday's victory against New York. He'll expect drive and commitment from the opening whistle, especially given the physical approach that Chicago has traditionally used to good effect against D.C."The break was, I think, important for a couple of guys who were carrying little [injury] things," he said on Tuesday. "But also mentality -- you have to be able to take a couple days to yourself and clear your mind and make sure you're ready to get back at something, especially the importance of this game, playing for first place."