Williams was denied a 24th Grand Slam title of his career after a 6-2 and 6-2 loss.
Halep needed less than an hour on the court to win his second major title of the tournament after the success at the French Open last year.
The Romanian was like a wall in front of Williams as she showed defensive skills to Novak Djokovic.
And Williams admitted that she could not have done otherwise.
"She literally played out of her mind, congratulations Simona," said Williams.
"It was a bit expensive for the headlights for me.
"Whenever a player plays at this point, you have to take off your hat and nod to him."
Williams is still a Grand Slam title behind Margaret Court's all-time record.
But she promises to continue fighting to strengthen her legacy.
"I just kept fighting and enjoying this sport," she added.
"I like to come here and play in front of you, it was really fun.
"My team is amazing, thank you all for all the support and I love you all."