The CEO of the Nasdaq stock exchange says it is ''humbly embarrassed'' by its bungling of Facebook's hugely anticipated debut as a public company.
Robert Greifeld told media there was no indication the delay contributed to the underwhelming performance of Facebook's stock, which ended at $US38.23 (NZ$50.34) - just 23USc above where it listed.
Facebook's stock was expected to start trading at 11am Friday (US time) but didn't open until 11:32am, and some investors didn't learn for hours whether their orders went through.
But Greifeld called the social network's first day of trading ''successful''.
He said late order cancellations caused a glitch and that the Nasdaq board met over the weekend and plans to change its IPO auction process.
The US Securities and Exchange Commission is investigating.
The surprisingly weak debut of a stock that analysts had predicted would climb between 10 and 50 percent is not likely to dent the business prospects of Facebook, which boasts 900 million users and is upending business practices and social relationships around the world.
But the unexpected developments were a clear setback for Morgan Stanley, the lead underwriter on the deal, which sources said was forced to defend the US$38 price level by buying shares on the open market.
Many market participants said they expected the stock to remain under pressure this week.