The day after declaring her impending retirement, Serena Williams was full of emotion and admitted it had been a "pretty interesting 24 hours" for her.

Williams revealed on Tuesday in an article in Vogue that "the countdown has begun" for her retirement with this month's US Open set to be the 23-time major winner's last tournament.

The 40-year-old was knocked out of the Canadian Open on Wednesday by Belinda Bencic 6-2 6-4 and spoke after the match for the first time publicly since declaring her intention to retire.

"It was a lot of emotions obviously," Williams said during the on-court post-match interview.

"I've loved playing here [Toronto], I've always loved playing here. I wish I could have played better but Belinda played so well today.

"It's been a pretty interesting 24 hours."

Williams, who won the first of her 23 Grand Slam titles way back in 1999 at the US Open, was emotional about the reception from fans to her announcement.

"It's just been so memorable," Williams said.

"Like I said in my article, I'm terrible at goodbyes. But goodbye, Toronto."

Williams has already been named on the entry list for the US Open, which starts at Flushing Meadows at the end of August.

The former world number one had claimed her first WTA singles win in 430 days on Monday when she defeated Nuria Parrizas-Diaz in preparation for her US Open farewell.