Madrid, Istanbul and Tokyo made their pitches to IOC members, hoping to seize the momentum in the final two months before the vote.
This was the first time the cities had the chance to present their case directly to the electorate and Madrid made the most of it, generating a buzz that could make the race tighter than ever.
Counted out by many a few months ago because of Spain's severe financial troubles, Madrid hammered home the message that it offers a low-cost, no-risk bid.
"If you're grading performance, Madrid did the best in terms of the message and delivery of it," senior Canadian IOC member Dick Pound said. "The star of the day was the prince. It was his content, his delivery, his genuineness.
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"Those who might have Madrid as a distant third would now be rethinking that."
Other members also cited the 45-year-old prince's appearance as the highlight of the day. Britain's Craig Reedie, who wrote a technical report evaluating the bids, said Madrid "lifted their game."
It was at a similar meeting in 2009 that Rio de Janeiro grabbed the momentum in the race for the 2016 Games, but members said there was probably no dramatic turn this time to decide the winner.
"I think it's less clear than before," Reedie said.
Istanbul's presentation passed off with scant mention of the anti-government protests that swept the country last month, while Tokyo cited its financial strength and the Olympics as a symbol of Japan's recovery from the 2011 earthquake and tsunami.
Spanish IOC member Juan Antonio Samaranch Jr, who was part of those two bids and sits on the 2020 committee, said it was too early to judge the impact of the presentation.