"I'm not going to lie. It hurts bad," she conceded after a 7-5 6-7(6) 6-1 at Flushing Meadows. "It's okay. I did everything I could. I gave my heart. I fought as hard as I could.
"I lost to a great champion and I'm still going to have my head up."
After losing the first set, Azarenka produced a phenomenal second where she fought back from 1-4 and 3-5 down to force a decider at an electrified Arthur Ashe Stadium as Williams twice blew chances to earn a straight-sets victory.
But the 24-year-old Azarenka was unable to carry momentum into the deciding set as Williams, who had thrown her racquet into her chair at the changeover, took care of the third set to complete victory in two hours and 45 minutes.
"She really made it happen," Azarenka said.
"There was no letdown. It was a moment in the third set that the momentum changed a little bit, and I kind of felt like I lost that momentum. In that particular moment she was tougher today. She was more consistent and deserved to win."
The ball-striking was superb from the top two players in the world. Azarenka showed enormous determination to recover from two breaks down in the second set, but her fightback took its toll.
Come the third set, she was running on empty.
"It was raising from the first point, the tension, the battle, the determination," Azarenka said. "It felt from every point, it was rising, the level."
Azarenka paid tribute to Williams after the American won the 17th Major singles title of her career.
"Well, there's one word," Azarenka said of Williams.
"She's a champion, and she knows how to repeat that. She knows what it takes to get there. I know that feeling, too. And when two people meet who want that feeling so bad, it's a clash. That's what happens out there with those battles.
"And in the important moments, it is who is more brave. Who is more consistent. Who takes more risk. You can never play safe."
Williams was reaching the pinnacle of her career, said Azarenka.
"She's playing definitely her best tennis right now. It really shows how focused and how composed and how much she can raise the level," she added.
"That's just exciting for me, to be able to compete against that type of player who can be the greatest of all time. I'm playing against that person in the finals of Grand Slams."
The 24-year-old said she was determined to view her US Open as a positive when she visited her family in Belarus this week.
"You cannot sit and say, 'Oh my god, this is the worst thing that could have happened to me.' Because it's not. I just want to take the positive and see the light at the end of the tunnel."