* U.S. jobless claims unexpectedly fall to 5-year low * Strong bids at $15 bln 10-year TIPS auction By Richard Leong NEW YORK, Jan 24 (Reuters) - U.S. Treasury debt prices slipped on Thursday after data showed first-time filings for weekly jobless benefits fell to a five-year low, raising hopes of an improving U.S. labor market and paring safe-haven bets on government debt. Initial strength in U.S. blue-chip stocks, together with a temporary extension of the federal debt ceiling, also undermined Treasuries prices, as the benchmark S&P 500 index briefly climbed above 1,500 for the first time since late 2007. The unexpected drop in jobless claims "caught some people by surprise and exposed some longs," said Tom Roth, executive director of U.S. government bond trading at Mitsubishi UFJ Securities USA Inc in New York. Benchmark 10 year Treasury notes were 5/32 lower in price to yield 1.845 percent, up 1.7 basis points from late on Wednesday. Bond prices bounced back from their session lows after strong demand at a $15 billion auction of a new 10-year Treasury Inflation Protected Security issue.