The Mets' 3-0 loss to the Cardinals at Shea last night was in the books. So was Philadelphia's win over Atlanta. And every bit of the seven-game lead that the Mets on Sept. 12 had completely vanished. The players, clearly shaken but trying to stay optimistic, were whispering about "fighting" and "not giving up" when Willie Randolph cruised through and spoke loud enough to make sure everyone heard him. That's when the normally stoic Randolph decided to make a bold claim. "We're gonna win this thing!"