Williams defeated Sharapova 6-4, 6-1, and will now face Agnieszka Radwanska in the semifinals. Williams is 8-0 against Radwanska. In fact, Williams has a lopsided winning record against all of the top contenders.
Yet doubters emerged at this year's Aussie Open. It's as if one upset loss at the 2015 U.S. Open negated a record-breaking, legendary resume.
Perhaps Williams has been dominating so long that folks figure something's got to give. And it will.
But based on the way Williams is playing, she's not giving up anything anytime soon.
Prior to the Australian Open, several tennis journalists raised questions about Williams' form. The 21-time Grand Slam champion hadn't played an official match since losing to Roberta Vinci in the semifinals of the U.S. Open last August.
Williams withdrew from the Hopman Cup with a knee injury. Pre-tournament buzz began circulating about whether she was healthy enough to make a run at a 22nd Grand Slam title.
Despite her attempts to squash any doubts, the doubters came out. How quickly they seemed to forget Williams was coming off a three-Slam year, not to mention she had just won Sports Illustrated's Sportsperson of the Year.
So it was somewhat shocking so many tennis experts had doubts about Williams' ability to win this year in Melbourne.
An ESPN.com preview of the Aussie Open was titled, "Seriously? Little Faith in Serena Williams Down Under." That's because of the 12 experts, which included Chris Evert, Cliff Drysdale, Patrick McEnroe and several tennis writers, only two picked Williams to win the tournament.
Most, including Evert, picked Victoria Azarenka, who might well win. But Williams is No. 1 and has won the Australian Open more than any female player in the Open era.
In a pre-tournament interview with Reuters (h/t the Daily Mail), Evert predicted Williams would struggle in 2016. She also thought Azarenka was the player to watch: "I think she's a player we should be talking about and focusing on right now...She's got to be one of the two or three favorites for winning the Australian Open. I always thought she has a champions' mentality."
Williams has a 17-3 record against Azarenka and has never lost to her in a Grand Slam. Yet the consensus is it's Azarenka's tournament to lose?
Oddly, even with Williams' 17-match winning streak against Sharapova, much of the buildup to this match was about how Sharapova might pull off the upset.
Danielle Rossingh, a contributor to Forbes.com, wrote about the three reasons why Sharapova may end the 12-year losing streak.
Reuters' Ian Ransom ran a story about how Sharapova's serve "fires up in time for Serena." An article in espnW echoed that point about Sharapova's serve giving her a slight advantage in a matchup against Williams.
Wait a minute. Williams has what most consider the greatest serve in the history of women's tennis, and Sharapova, a double-faulting machine, has the edge?
Prior to their match, Sharapova had 52 aces to Williams' 25. But Sharapova also had two three-set matches. Williams was breezing through her matches, ending her third-round match in 44 minutes.
After Williams' win over Sharapova, a reporter asked her to explain her dominance over the Russian. Williams responded (via AusOpen.com), "I don't know. Something about her game. I like the way she hits the ball. Plus, when I play her, I know automatically I have to step up my game."
In sports, the reigning champion is usually afforded the benefit of the doubt until someone comes along and knocks off the crown. No matter how battered and bruised the New England Patriots looked, they received that respect.
This emphatic win should serve notice that Williams is in championship form. She's yet to drop a set and just beat a five-time Grand Slam champion for the 18th consecutive time.
Next up she faces Radwanska in the semifinals. Williams told reporters Radwanska brings an entirely different set of challenges: "She presents a completely different game, an extremely exciting game. So I think it will be a long match and it will be a good match to see where I am."
Williams has never lost at the Australian Open after reaching the semifinals. Perhaps the biggest threat left is Azarenka, who faces Angelique Kerber on Wednesday. Williams has a 5-1 record against Kerber. She is 2-0 against Zhang Shuai. She's never faced Johanna Konta.
Konta could be the wild card. The unknown seems to unsettle Williams far more than familiar foes.
Regardless, there will be doubters. But not everyone.
Wimbledon champion Marion Bartoli, also a commentator for Eurosport, told USA Today's Nick McCarvel, "Last year here Maria was very close and Serena had to come up with her absolute best, but that's why she's No. 1. [Serena] has to come up with her absolute best when she needs to. She's not No. 1 for no reason. That's why she's so dominating."