"It's all about the wallet," Cook told the crowd. "Our vision is to replace this."
Apple's latest victim could be cash itself.
A quick video presentation showed a woman fumbling for her card at a till, working her way through junk in her bag, before eventually swiping and walking away with her goods.
Apple Pay would make the whole process much easier, we're told. Simply pull out your phone, tap the register, and you're away. It makes some sense, at least for the shoppers who already wander around with phone in hand.
To get started, Apple is targeting the plastic that fills our pockets.
The iPhone 6 and 6 Plus will both be Apple Pay compatible. Owners of either device can hold their card details in a digital wallet, and tap at the till to pay for goods.
By the end of this segment, Cook had received both laughter and applause, although more muted than that for the company's other re-leases.
Perhaps some of the announcement's significance was lost, as the concept of contactless payments fell flat on a US audience unfamiliar with them.
The real fanfare was on Wall St.
Within minutes, Cook had wiped huge amounts off the values of Apple Pay's would-be rivals. Shares in PayPal owner eBay fell by almost 1.7 per cent. After the keynote speech was over, eBay's losses extended. By the next morning, its shareholders were left 6.3 per cent poorer.
News that Apple was stepping into the ring had knocked US$4.2 billion ($5.16 billion) off the value of a single rival.
It's an idea that has been tried before, but has fallen flat. Now the world's financial institutions think Apple can take on cash and plastic.
"We love this kind of problem," Cook said.
Apple is no stranger to upsetting expectations. Four years ago, Steve Jobs, then chief executive and a gifted presenter, was met with near universal criticism when he pitched the new iPad range.
Tablets had existed before, and consumers had rejected them, how could Apple change that? The critics were wrong. Now, the devices are close to ubiquitous, with 170 million units sold by last October, while an ecosystem of cheaper tablets has emerged.
This week was Cook's first chance to make his mark. The Apple Watch is the first new product line to be announced since Jobs died, yet the firm's steps into the world of payments may be how the current Apple boss cements a legacy.
Cold, hard cash has been with us since at least the 7th century BC, when the Lydians began using coins made from a naturally occurring mixture of gold and silver, called electrum.
Since then we've developed a myriad of financial institutions, from the first forms of lending to an array of microwaves that allow investors to trade at blistering speeds.
But we haven't been able to shake our attachment to carrying lumps of metal around. The first big myth about cash is that it's cheap, that the transaction costs of using paper and coins are low.
David Birch, a director of the electronic payments specialist Consult Hyperion, will assure you that's nonsense.
"It isn't just that cash introduces inefficiencies, and that we'd have a much more efficient payments system without it," Birch said.
It's that cash imposes its highest transaction costs on the poor, he argued. Those on low incomes are typically time poor too, and cash eats into our day.
Cash costs the US economy US$200 billion a year, according to a 2013 study by Tufts. Tax evasion, theft, and even the time it takes to obtain cash play a role. On average US shoppers spend 28 minutes a month travelling to ATMs to withdraw cash.
Imagining easy wins for a society with just electronic money isn't hard. Take the hand-held barcode scanners that used to be found in major supermarkets.
In the future, you could tap a dispenser to release a scanner, then walk around the store scanning items as you go. Then, when your shop is over, forget going to a cash register. Just tap the scanner again with your phone as you leave it at the door, paying as you exit.
Cook has brought us a step closer to the much heralded end of cash. But if this technology - near field communication (NFC) - works so well, why aren't we all using it already?
Some of us are. But there hasn't been a huge deal of market penetration. Retailers have been slow to support contactless payment, as they have little reason to. There's no point providing an opportunity for a handful of customers.
Analysts had all but written off widespread NFC use.
Apple's vast scale effectively fixes NFC's first big problem straight away. The iPhone 6 and 6 Plus are expected to sell in huge volumes, likely to break all of Apple's smartphone sales records.
Market research suggests that the new devices are the most anticipated of all time, as consumers upgrade from their iPhone 4 and 4S models, which are the best-selling on record on an accumulated basis.
And Apple's iTunes platform, which shoppers will have to sign up for to use Apple Pay, already boasts 800 million users.
Secondly, Apple has been a trend- setter for close to two decades.
The company's art has not been in developing entirely new technologies, but in refining existing inventions, and repackaging them in a way that makes them genuinely appealing to customers.
It's not the technology that makes the company's play interesting, but its brand. "They have mindshare," Birch said.
"Apple has effectively legitimised the idea of using your mobile for payments. That makes a world of difference.
"Apple tells people this is okay, and it changes people's opinion."
Consumers and other businesses alike are now looking to fit Apple Pay into their plans. The large names that Apple has already signed up for its US launch this October - including McDonald's, Disney, Starbucks and Whole Foods - could end up doing a lot of the dirty work.
Those retailers will want to see a healthy return from refitting their stores to achieve compatibility with Apple's new technology, so they will want to ensure that customers know they can pay with their iPhone, and understand how to.
Apple has also assembled a powerful roster of banks and payment companies - Visa, Master- Card and American Express are all signed on for launch - that account for 83 per cent of all credit card volumes in the US.
This could be a turning point.
Two things Apple has kept in mind are privacy and security, especially after recent vulnerabilities in its iCloud storage system led to the leaking of private photos. While iCloud was protected with just a password, the secure element in each phone should keep payment information safe.
Apple never sees the user's credit card information, and if you lose your phone, payments from the phone can be suspended remotely. No credit card cancellations would be necessary.
The move has been well timed. Many US retailers are upgrading their registers as shoppers say goodbye to swiping cards, a practice that's been around for nearly 50 years.
Now that he has given the payments industry a welcome shove, Cook might want to look back towards a familiar problem. Customers want phones with longer battery lives.
If Apple can't find a way to make their smartphones last longer, users could find themselves stranded without both their phone and their wallet when their device gives up.
