Mr. Ryan watched in horror as the bizarre scene played out before Hollywood’s biggest stars and tens of millions of people watching around the globe. In a dizzying turn of events, his firm, which normally occupies a back seat at the glamorous event, was suddenly at the center of one of the most sensational stories in Oscars history.

“I knew something was up,” he said in a telephone interview on Monday, zeroing in on the discordant moment when he noticed two of his employees interrupting the best picture acceptance speeches. “It’s not their job to come out on stage.”

As the magnitude of the gaffe set in, Mr. Ryan went into crisis-management mode.

“What was going though my head at the time was, ‘We have to get to the bottom of this, and if we made a mistake, we’ll own up to it,’” Mr. Ryan said. “My philosophy in life is, bad news doesn’t age well.”

Reaction to the mistake has been swift and harsh.

“The accountants have one job to do — that’s to give Warren Beatty the right envelope,” Leslie Moonves, the chief executive of CBS, said in a videotaped interview after the show, which was broadcast on ABC. “That’s what these people are paid a lot of money to do. If they were my accountant, I would fire them.”

On Monday, the hashtags #envelopegate and #Oscarfail were trending on Twitter, and PwC, a business that markets its services to other businesses, was newly on the tip of many consumers’ tongues in an unforgiving fashion.