A new analysis shows that borrowing costs for the U.S. government have fallen, contrary to the prediction of some economic experts that they would markedly increase after the country's credit rating was downgraded.

A U.S. business news outlet, Bloomberg, reported Friday that the $72 billion worth of notes the government auctioned this week collectively carried the lowest interest rate ever, saving American taxpayers $647 million in interest payments.

Standard & Poor's a week ago trimmed the country's AAA rating to AA-plus, an indication that its analysts viewed the U.S. government as a slightly riskier bet to repay its debts. Two other financial services firms continued to give the U.S. their top ratings.

The Standard & Poor's downgrade prompted fears by some analysts that the government's burgeoning long-term debt level would soon worsen, costing the U.S. hundreds of millions of dollars more to run the government.

But the opposite happened, with the government selling the three-, 10- and 30-year bonds at an average interest rate of 2.13 percent, well below the former record of 2.59 percent in early 2009.

Analysts said the record-low interest rate on the notes showed that investors were not concerned about the Standard & Poor's action, and continued to view U.S. bonds as among the safest investments in the world. Foreign central banks and large investment funds were among those who bought the government debt.