“I have been working on finding a calm mind and keep the body going,” the Belarusian said in an on-court interview. “She dug me in a big hole in the first set. I needed to find energy to climb out of the hole and it wasn't easy.”
Williams, who has been stuck on 23 Grand Slam titles since winning the 2017 Australian Open, said the defeat was “obviously disappointing”.
“At the same time ... I did what I could today,” she said.
“I feel like other times I’ve been close and I could have done better. Today I felt like I gave a lot.”
Six-times US Open champion Williams came out firing winners from all sides of the Arthur Ashe Stadium court while Azarenka struggled with her serve, committing four double faults in the first set and winning just six of 15 first-serve points.
She also had 10 unforced errors and appeared increasingly frustrated, with a microphone catching her muttering a pair of expletives at herself before Williams took a 4-1 lead.