A victory at Robert F. Kennedy Stadium on Saturday would seal the series, but the Red Bulls would also advance with a draw, a loss by no more than one goal or even on the away-goals rule (new to the M.L.S. postseason this year). An early goal by New York would put D.C., which finished first over all in the conference, under enormous pressure.

After starting 18 different defensive combinations through the M.L.S. season, Petke has settled on a steady back four of Eckersley on the right, Roy Miller on the left, and Jamison Olave and Ibrahim Sekagya in the middle for the past three games. Over that span, the Red Bulls have scored six goals and allowed only one in winning three critical games.

For Petke, quality, not continuity, is the issue in defense.

“Continuity is a beautiful word and it’s intriguing to write about in the papers, but to me it means nothing,” Petke said. “I’ve said it all along, cohesiveness, I guess you could say perhaps to a lot of people is important and it’s important to me if the four people being cohesive are doing their job, but I will not sacrifice the team or us possibly getting a result because I’m saying I have to stick with continuity, I have to stick with the same players.”

For Eckersley, whose contract expires at the end of the year, the fall from grace was taken as a personal challenge.

“I think it starts on the training field,” he said. “You have to work. I didn’t go home and sulk all day, but mentally it was really draining. I started getting a few minutes during the Concacaf games.”

While the Red Bulls seem to have settled on the same four guys on the back line, Petke was quick to credit, in a recent conference call, the solid play of Dax McCarty and Eric Alexander, the team’s two holding midfielders. Still, he came back to the quality of the back four.

“If you look at all four of them as individuals, you look at Roy Miller, who is one of the best left backs in the league, so he is solid out there.” Petke said. “You go next to him with Sekagya, the last month and a half I think has been one of our most important players. He just reads the game so well and he brings a wealth of experience and he’s got a phenomenal attitude and he’s a big leader back there. Olave next to him is one-on-one defensively to me the best defender in the league, so we need that type of fighting back there and that type of workmanlike attitude out of him. And then the right back was interesting you know, we went through a number of right backs this year.”