Williams fired down 24 aces to reach the final and Azarenka, seeded second and the Australian Open champion, was powerless to resist despite improving in the second set.
"I was just trying to fight because I knew I was going to have a chance sooner or later," the Belarusian said.
"Before that she was playing really well. The serve is just that one difference that brings her to the higher level."
Azarenka struggled to compete during the first set but she improved in the second, breaking back to force a tiebreak.
"I just tried to fight and tried to stay in the moment," she said. "If I have a chance, just try to grab it. That's what I did. It was really close, but it wasn't my day today."
Azarenka admitted that Williams's serve was a lethal weapon.
"Well, she serves 200 (kilometres an hour)," she said. "That already makes it difficult. I don't see anybody else serving like this on the tour. She places well. I don't know how many lines I got today.
Azarenka said she was optimistic about the future, with the world number one spot very much in her sights.
"There is no point to sit and cry how unfortunate I was because she played great," she said. "I just have to give her all the credit because she did her job.
"I was just trying to get the ball back as many times as I could, but it wasn't enough today."
Azarenka said she expected Williams to secure her 14th Grand Slam title in the final against Agnieszka Radwanska on Saturday.
"I think Serena's going to win, but Agnieszka is a very good player," said Azarenka. "It's not easy to get to the final, so anything can happen."