Serena Williams and the changing tennis landscape

Kuznetsova: 'Thrilled' with win over Serena (1:07)

Svetlana Kuznetsova reacts to defeating Serena Williams in the fourth round at the Miami Open. (1:07)

MIAMI, Fla. -- This was the event in which Serena Williams was supposed to regroup and recharge her dominance gene.

She was never supposed to lose her fourth-round collision with No. 15 seed Svetlana Kuznetsova -- not even in light of the world No. 1's recent struggles. She was back on her home turf in Miami, where she had accumulated 20 consecutive wins and three straight titles.

Instead, Williams' game wilted in the 91-degree heat and humidity she professes to love, handing Kuznetsova a 6-7 (3), 6-1, 6-2 win.

Williams seems to be going in two directions at once -- barreling toward Steffi Graf's ultimate Grand Slam prize (a quest with 20 years of momentum behind it), while slowing down and finding it harder and harder to marshal her enthusiasm on a day-to-day basis, or in the case of her match Monday, a set-to-set basis.

After a terrific start, Williams ended the Miami Open with 55 unforced errors (three times Kuznetsova's output). That lethal serve of Williams pumped out 13 aces but also eight double faults -- some at critical times. Most telling, Kuznetsova won 61 percent of her second-serve points, while Williams won just 39 percent of the second serves she hit.

Williams' postmatch meeting with the press lasted all of 2 minutes, 40 seconds, during which she conceded her movement was lacking, but offered no explanations other than denying that the sweltering conditions were to blame.

When pressed on the issue, she took umbrage: "It's not appropriate to criticize my movement right now. I did the best I could today. I can't win every match. These players, they come out and they play me like they've never played before in their lives. I have to be 300 percent every day."

Williams hasn't won a title since Cincinnati last August, her longest drought since 2012. Yet nobody has rebounded more fiercely and confidently than she has. It's easy to lose sight of that in the wake of all the drama that attended her quest for a calendar-year Grand Slam last year. Alternately overwrought and detached, her anxieties are communicable. But wait.

"You say drama when somebody is a No. 1 [and] who is probably one of the greatest in the history of athletics," Kuznetsova said after her win. "This is drama? For me, this would be miracle of the year. Serena struggled little bit [this year] probably because she lost the Australian Open. But I mean she is still No. 1, and she still plays great. I don't see much to be depressed about."

Williams was stung by the loss, but she was hardly the only marquee name to leave Crandon Park disappointed on bloody Monday. Agnieszka Radwanska, seeded No. 3, was beaten in three sets by No. 19 Timea Bacsinszky.

Soon after, an ATP fourth-round match sent shockwaves through the grounds as No. 26 Grigor Dimitrov outmuscled No. 2 Andy Murray 6-7 (1), 6-4, 6-3. In a Serena-like performance, Murray committed 50 unforced errors.

That's just one of the factors that might make this a wild year in tennis, perhaps even a transformational one. Williams is still without a title in 2016, as are Murray, Roger Federer and Rafael Nadal.

Nadal played well in Indian Wells, but he was obliged to quit during his match here with Damir Dzumhur, overcome by dizziness and disorientation.

Federer, a very strong No. 3 at the start of the year, hasn't played a match since injuring his knee a day after he lost in the Australian Open semifinals. True, he was merely unlucky to contract a stomach virus that forced him to pull out of the Miami Open before his first match. But Federer, who, like Williams, is 34, had a firm game plan when he made his 2016 schedule, and that's been turned topsy-turvy.

Even Murray, whose consistency improved dramatically over the past 12 months, seems less reliable. He lost early at Indian Wells as well. Given that he's one of the Big Four responsible for the recent stability in the game, he wasn't enamored of the idea that this might be a year when the old order is shaken up. A sentiment Williams would likely share.

"I don't know. I guess it's possible," Murray said after his match. "But I think over the last couple years, there's been sort of periods like this. It hasn't sort of turned out that way. I hope it's not the case for my sake. Yeah, I think I need a little bit more evidence than one or two weeks to suggest that."