Serena Williams may pack a knockout punch and be the greatest player ever to grace women's tennis, according to Victoria Azarenka, but the world number two insists she is steadily closing the gap.
Azarenka suffered another bruising loss to the mighty American in the US Open final earlier this month in a repeat of the 2012 championship match in New York.
But the Belarusian quickly climbed off the canvas, saying she was over it in 24 hours.
"Serena is the best ever to me," Azarenka told AFP on Sunday in an interview before her opening match at the Pan Pacific Open in Tokyo.
"I cannot judge somebody who I never played before but for me overall the game of tennis has elevated and the evolution of the game raised up so much that it's hard to compare.
"It's like comparing Muhammad Ali and Floyd Mayweather," the 24-year-old added.
"How can you compare two eras? They're both the greatest in the world but who was the better boxer?"
Despite defeat at Flushing Meadows and the enduring brilliance of Williams, Azarenka was in buoyant mood.
"Serena is playing the best tennis of her life and so am I," she said.
"It's been really noticeable the gap from last year we have in the matches has minimised. I've beaten her twice this year. No one else has done that.
"It's just exciting to be in the era of somebody and competing with somebody who is considered the best ever and being their toughest opponent."
Azarenka, who has held the world's top ranking, called her 7-5, 6-7, 6-1 defeat at the US Open a "learning experience" but pointed to two victories over Williams in 2013 as evidence she had the game to threaten the dominance of the 17-time grand slam singles champion.
"Serena is always improving," twice Australian Open champion Azarenka said of her nemesis, who turns 32 this week.
"This is the beauty of the competition. It's a healthy competition and you have to rise to the occasion and really step it up (to) the next level if you want to be up there. Serena's still not done."
Azarenka, whose head-to-head record against Williams is still a lopsided 3-13, said of her latest schooling: "I was over it the next day.
"I have a 24-hour rule, win or lose. You have to get up and keep going."
Her latest tussle with Williams was also a noisy affair, the ferocity of their hitting pushing the grunt-o-metre off the scale.
"In tennis it's weird because everybody keeps complaining that people grunt but if you watch any other sport (they do)," she said with a laugh.
"It's the same with the guys' tennis. You watch (Rafa) Nadal and (Novak) Djokovic. I mean how less intense was that (US Open final)? And nobody talks about it. This doesn't make sense in my head.
"You take each other to the limit of battle and give 100 percent in every point and when you play in the final of the US Open against a player like Serena you've got to do that because that's what she does and that's how she pushes you."
Preparing for Tokyo, Azarenka showed her playful side with a parody of American pop diva Miley Cyrus's controversial MTV Video Music Awards performance on her Instagram account.
"I just thought it was a really funny video to do," she said of her effort at 'twerking'.
"I'm never afraid to show my personality. I'm an entertainer myself. I was a little shy before. Now I'm out of that zone I just want to show my world with my fans."
Weighing in on the debate raging over Cyrus, Azarenka smiled: "It's up to everybody. I have different tastes. She's definitely not my role model."