The most surprising aspect of the Washington Nationals is not that they are in first place in the National League East or that they have a better record than any wild-card contender, although those facts certainly challenge the limits of baseball imagination. What's most mind-numbingly improbable is not that they have overcome 14 players on the disabled list a total of 15 times, losing 490 games to the DL already this season. And, in their latest installment of "The Nats did what?!" it's not even that they completed a three-game sweep of the Marlins yesterday at RFK Stadium before 40,995 fans despite facing flame-throwing A.J. Burnett without their three best-known hitters -- Brad Wilkerson, Jose Guillen and Jose Vidro -- in the starting lineup.

What's most amazing about the Nationals -- and they have reached the point where amazing is not too strong a word -- is the quality of the opposition against whom they have amassed their 31-26 record. Of the Nats' 57 games this season, a stunning 47 have been against teams that currently are over .500. Against the game's nine worst teams, they've played only six games.

Not only do the Nats play in the toughest division in baseball where all five clubs have winning records, but almost every time they step out of the NL East, the sadistic schedule maker sends them to play contenders in St. Louis, Los Angeles or Arizona. For the Nats, a breather is playing a solid middle-of-the-pack team such as the Cubs, Blue Jays or Brewers.

Over the decades, other plucky preseason underdogs who were, like the Nats, universally picked for last place have managed to stay over .500 for a couple of months, and some have probably even done it despite the most injuries of any team in baseball. But has any such team ever fought its way to its division lead while playing 82 percent of its games against winners?

After what the Nationals have accomplished, going 7-3 in their last 10 games against the cream of the NL -- the Cardinals in St. Louis, then the division-favorite Braves and Marlins at RFK -- it's time to get off the fence. The Nationals are real.

Will they still be contenders in September or even August? For that matter, will they even be able to maintain their ferocious focus this week as they face the first soft patch in their schedule -- six games at home against the way-under .500 A's and M's? Nobody knows. But it is no longer fair to damn the Nationals with the faint praise of "chemistry" or discount their success as the product of the early-season inspiration in a new town in front of large stands-bouncing crowds.

There's pitching talent here, veteran leadership and stubborn hitters who seem to need half the game to figure out how to mount an attack, yet repeatedly erupt in the late innings, producing 21 come-from-behind wins already. The Nats don't seem to start playing until after the seventh-inning stretch. Yesterday, they trailed 2-0 when the PA system played, "Take Me Out to the Ball Game." Even old Carlos Baerga said, "I didn't think there was any way we were going to beat Burnett, the way he was throwing." Burnett was so overpowering that Manager Frank Robinson had the scoreboard stop posting the speed of his 97 mph fastballs because "I was getting sick of looking at it."

Yet, in a blink, the Nats scored three runs in the seventh off Burnett, including a game-tying RBI by Baerga, who was hit with a pitch with the bases loaded, then plated three more on a homer by rookie Ryan Church in the eighth. Baerga's self-sacrifice of a bruised knee would seem unremarkable, yet he was the first player in the NL this season to "take one for the team" with the bases loaded. Afterward, he sat proudly at his locker with a comically oversized icepack on his wounded knee.

Across the entire field, there is exceptional Nationals defense. Yesterday, shortstop Cristian Guzman saved a run with as spectacular a diving stop in the hole and long throw to first base as you'll ever see. Every other infielder made at least one remarkable play. Brian Schneider threw out a key base stealer. And Guillen, called on for a pinch-hit single, made a perfect relay throw that prevented a go-ahead Marlins run from being waved home.

However, perhaps the hardest of all the Nationals' gifts to pinpoint is their clear team-wide understanding of how to play tight one-run games. Their attention to fundamentals has been a delight. "When somebody doesn't do something the right way, somebody in here tells them about it. Frank and the coaches don't have to call a meeting," said Baerga.

It's common to see three kinds of Spring Surprise teams. The first hustles for a couple of months but has a June-swoon reality check. The second type, and the Nats may still fit this mold, play with resiliency for two-thirds of the season but in the heat of August, wilt and regress until much of their good work is forgotten. The third and rarest variety, like the '89 Orioles, add a crucial player or two during the season and dazzle everyone, except themselves, by staying in the hunt until season's end.

Many still think the Nationals are a perishable team with an expiration date stamped on its back. But, after this remarkable week of comeback wins against the Braves and Fish at RFK, they still smell remarkably sweet. Asked what happened to the Marlins, Florida pitching coach Mark Wiley kept it simple: "In this game, sometimes injuries and all the other things people talk about don't matter. When you're rolling, you're rolling. And right now, they're rolling."

When the Nats left Cincinnati on May 25 after losing five of six games, they faced as stern a 10-game test as you could ask a team coming off a 95-loss season. After two more losses in St. Louis, they were reeling at 24-25. How long would the slump last? How many weeks of good work would it erase? How deep a hole would be dug?

Baseball (repeat in unison) is a game of streaks. What ignites the next one -- good or bad -- is often a mystery. This time, however, the turning point was obvious. Livan Hernandez stopped that slump with a 3-2 win at Busch Stadium. Home sweet RFK beckoned. And a slump turned instantly into a streak.

Now, as happens continually, the baseball question on the table is completely reversed. How long would the Washington road-trip slump last? The answer was delivered: not long. Now, how long will the homestand winning streak be extended? Will those six opportunities against Oakland and Seattle be maximized? Contenders stretch their streaks in such circumstances.

At least most Nats are talking the right talk. Told that his team was in first place, Robinson said, "Okay, that's nice. We need to keep our heads the same hat size."

"It's only June. Don't get cocky," said Schneider. "We're proud. But we have so much more to accomplish."

How much more?

Yet another question about the first-place Nationals that few could have imagined on Opening Day.