Will an NFC payment terminal activate Apple Pay on an Apple Watch just like it does with an iPhone? With an iPhone 6 or later, you can bring the sleeping phone near an NFC payment terminal, and the phone will wake automatically to the Wallet, prompting a Touch ID authentication for the default Apple Pay card. Alternatively, the home button can be double-clicked while the phone is asleep to go straight to the Wallet in order to choose an Apple Pay card to use.

With an Apple Watch, the side button can be double-clicked to bring up available Apple Pay cards; the Watch is then brought near an NFC terminal to authenticate the transaction.

Is this first step always required, or can an unlocked Apple Watch simply be brought near to an NFC terminal to authenticate a payment with the default Apple Pay card, similar to the method in the first iPhone example?
You have to double-press the side button on the Apple Watch to activate NFC/ApplePay.

This is due to energy saving.