Treasury Secretary Henry M. Paulson Jr. left his suite at Manhattan’s Waldorf-Astoria Hotel last Sept. 15 after a sleepless night, feeling he’d done all he could to minimize the damage from that morning’s collapse of Lehman Brothers Holdings Inc., aides said.

At meetings concluded the previous evening at the Federal Reserve Bank of New York, Paulson and executives of the world’s largest financial institutions worked to head off two threats they anticipated in the wake of the biggest bankruptcy in U.S. history. The bankers spent hours trying to unwind Lehman-related credit-default swaps, bets made on whether companies will repay their debts. And with the help of a rule change by Federal Reserve Chairman Ben S. Bernanke, they were confident bank-to- bank loans would keep flowing.

“The general feeling was things were working,” said Phillip L. Swagel, Paulson’s assistant secretary for economic policy, who remained in Washington that weekend.

Nobody accounted for Bruce R. Bent. The 72-year-old graduate of St. John’s University in Queens, New York, created the first money market fund in 1971, the Reserve Primary Fund. He touted it as an investment so safe it would lull clients to sleep — so safe that, even with $785 million in loans to tottering Lehman, Bent and his wife had jetted to Rome that Sunday evening to celebrate their 50th wedding anniversary.