He did not lost his pace. He's not willing to run so much for whatever reason, but he's absolutely rapid. Not going for headers also. He just looks disinterested most of the time.
The answer is probably that Rashford and Bruno still had a lot of energy, they have high stamina level. Sancho is done pretty quickly, so is Eriksen. IMO this is key for ETH.
I honestly think Ronaldo will either not run or he will be subbed at half time on current form.
This. Rashford IMO feels too comfortable in this team, I hope good competition in either position will give him a kick. Otherwise it will be time to move him.