Darren Pearce said that Boxing Day, as well as December 27 and 28, was a "critical period" for retailers at the Sheffield shopping centre.
Six thousand shoppers had turned out to the centre by its 8am opening time, with the figure more than doubling to 16,000 just an hour later.
But the real keen buyers were outside Next - a store well known for its extensive post-Christmas price cuts - shortly after midnight, even though it was set to open at 6am.
Mr Pearce said: "People were queuing outside Next at 12.30am this morning.
"At eight o'clock there was 6,000 people at the centre when it opens and 16,000 by nine o'clock.
"Forty thousand people have been to the centre already," he said just before noon.
He added that the numbers were up four per cent compared to the same time last year, and that three million people had visited Meadowhall this December.
"We're really, really happy with the whole of Christmas, never mind Boxing Day," he said.
Despite gloomy national forecasts for business ahead of the festive period, he thinks that the traditional post-Christmas sales period is still hugely important for retailers.
He said: "I think we all know we all know we are living through challenging times, in terms of Brexit, but you have to continue investing in your product."
This time of year was seen as the "golden quarter" and is a "critical period", he added.
Mr Pearce believes that a £120m investment at the centre over recent years has boosted the consumer experience for shoppers.