Davy Arnaud's fourth-minute goal was the difference between the two sides in Washington as Petke was left to ponder the Red Bulls' underwhelming opening to 2014.
"Now, it's starting to creep in a little bit," Petke told reporters.
"It's still far from pushing the panic button, far from anything like that. But now it's getting to the point - especially after a game like this, a game in Chicago, a second half with Chivas [USA], where we just couldn't finish them off - that [we're] going, 'What the hell is going on here?'
"But overall, we're a good team and we have good players and we showed that tonight. All we can do is put it behind us and get ready for the next game."
Red Bulls skipper Thierry Henry was also left to rue the DC defeat which he feels was undeserved.
"I'm very critical usually, but if we carry on playing like we played in the second half, hopefully we can get on a good run because there's nothing to say about how we played," said Henry.
"After the [first] 30 minutes, I thought we passed the ball well, we created chances, sometimes we were a bit unlucky, sometimes we weren't unlucky.
"But we had the ball and I don't think we deserved to lose, but full credit to DC. They won the game."
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