The gnawing pressure of radically revised expectations finally hit the Washington Nationals last night in RFK Stadium.

Before this 5-4, ninth-inning, kick-in-the-gut defeat to the abysmal Colorado Rockies, the pressure of first place -- coupled with the delight at being the toast of Washington and the surprise of the sport -- had not disoriented the ex-Expos too badly. True, a two-week slump had gotten the team's full attention, especially an ominously symbolic "balk off" loss last Friday.

This time, however, the full meaning of having a Shock The World opportunity, and seeing it start to slip quickly away, grabbed the Nats right in the throat. They choked this one away. Gagged. Spit the bit. Here, take it, we don't want it.

All teams under pressure in pennant races choke a few games away. The $200 million Yankees did it for two months -- April and May -- when Alex Rodriguez fielded as if Theo Epstein had tied his shoelaces together. But the Nats, until recent days, and especially last night, hadn't had the misery of seeing themselves at their absolute comical worst.

"Ask them. Has the lead got their butts tight?" said Manager Frank Robinson. "I can't answer that. I can answer almost anything else. But I can't answer that." Then he muttered something like, "They don't want to hear what I'd say."

Every so-called Surprise Team has this harsh confrontation with reality. And it often happens as the 100-game mark approaches and it's actually possible to envision what sort of finish to the season might be enough to make the playoffs. For example, entering last night's game, if the Nats could finish 35-35, they'd win 88 games; considering how thoroughly mediocre the probable wild-card competition looks among the Phillies, Marlins, Mets, Cubs and Astros -- none of whom is more than three games over .500 or has outscored the league by more than a paltry 17 runs -- the Nationals' chances looked realistic.

"We don't have to be spectacular," said Robinson before the game, adding of the 35-35 goal, "we can do better than that."

However, being spectacular is not the Nats' problem at present. Among themselves, they have to confront how addled their play has become, how many fundamental mistakes they have been making for the last two weeks (3-9) and, finally, how the pernicious pressure has infected them sufficiently that it has even contaminated their trademark crisp fielding.

"Can't catch the ball. Can't execute," said Robinson. "Catch the ball and throw it. You shouldn't go into a slump in that."

This game's deciding play came in the top of the ninth with a Rockie on third and two outs. A routine grounder was hit to third baseman Vinny Castilla's left. Perhaps his aching left knee bothered him, though he wouldn't make that excuse. "I just missed it," he said. So did shortstop Cristian Guzman, who should have hit the dirt to try to keep the ball in the infield instead of trying to field it in position to throw.

As the ball trickled into short left field, closer Chad Cordero, almost the only Nats stalwart who hasn't been infected by the recent malaise, was charged with a defeat on an unearned run.

"Man, that was an ugly game," said backup catcher Gary Bennett. "I don't think the lead is making us tight. I have no reason to believe that. We're still in a good spot [in the standings]. As long as we realize that and don't panic, we'll be all right. It's easy to be happy when you're winning. Now we'll see if we're still a tight unit when we're going through a rough patch."

To understand the weight of this simple loss, consider that the Rockies' 8-36 road record is one of the worst in the history of baseball. And they played as badly as their record. A popup by Preston Wilson fell for a double that led to two Washington runs. An outfield throwing error gave the Nats another free tally. Washington got five walks, twice helping them load the bases.

Yet as decisive moments, weird things befell Washington. One Colorado runner who eventually scored reached first base on an infield hit because his shattered bat prevented Castilla from fielding his ground ball -- unless Vinny wanted to be impaled. In addition to three errors, the Nats had a passed ball and center fielder Wilson misplayed a long fly into an RBI triple.

However, the most snake-bitten play of the night sank its teeth into the Nats. Thanks to a Colorado error and a walk, Washington loaded the bases with one out in the fourth. Submarine starter Byung Hyun Kim, one of the game's zaniest pitchers, threw a ball entirely behind batter Brad Wilkerson. The pitch hit the backstop so hard that it rebounded to the Colorado catcher, who spun and picked the Nats' dumbfounded Brian Schneider off third base. Goodbye, rally.

"When things like that happen, you know it's not going to be your night," said Cordero. "It seemed like everything was going our way in the first half. Now, everything [bad] has come together at once . . .

"Hopefully, we can battle through this and stay somewhere close to the top."

All season Robinson said he wanted his team "to fly under the radar" as long as possible. But a 26-6 winning streak and a brief 51/2-game lead in the National League East on the Fourth of July will cause a great big blip on any baseball screen.

So, the sport now has the Nats in its sights. After blunderfests like this one, they'll be analyzed and evaluated, put under every microscope like an odd and fragile insect that's never been seen this late into the summer. What should be expected of such a team? By its fans? By those who run and manage the team? By the players themselves?

These Nats are certainly not the team that lost 95 games in Montreal last season. But, just as surely, they are not the near-miraculous club that went 50-31 in the first half of the season, a 100-win pace. The truth lies in between. But where? Everybody wants to know, "Whither the Nats?" Are they crumbling. Or just stumbling a bit?

Before this game, it was premature to fret about the Nats. Not anymore. If they aren't in a full-blown slump, it's mighty close. The Braves are on their heels. The weather and the pressure will only get hotter. This game demonstrated, beyond one night's score, that the Nats need to calm down considerably. Otherwise, high expectations will not remain a problem for too long.