Serena dusting off the rust at Wimbledon, but Riske poses a greater threat

Serena handles Suarez Navarro, advances to Wimbledon quarterfinals (1:21)

Serena Williams dominates Carla Suarez Navarro in straight sets to advance to the quarterfinals at Wimbledon. (1:21)

LONDON -- While her side of the draw was seeing upset after upset, Serena Williams -- having stormed into the Wimbledon quarterfinals and kept true to her projected pretournament path -- had an ominous warning for her remaining competitors: "I feel the rust is wearing off."

Williams spoke fresh from dispatching Carla Suarez Navarro in straight sets 6-2, 6-2 in under an hour on Court No. 1, but you sense she is still building, finding her natural rhythm and also doing her utmost to stay, as best she can, under the radar. All this against a backdrop on her half of the draw where world No. 1 Ashleigh Barty lost out to Alison Riske, who had never previously made a Grand Slam quarterfinal, and last year's champion Angelique Kerber had already bowed out.

Williams is going about her business in a tournament that is becoming harder and harder to map out.

When the first serves were sent down in anger on Manic Monday, it looked set to be a day of ticking boxes, to tee up the mouth-watering quarterfinal of Barty against Williams. Barty won the first game against Riske thanks to four straight aces. There was an inevitability; the sporting script was neatly planned out and being kept to. Barty, who before facing Riske had not dropped a set since the French Open semifinal, took the first 6-3. But then her first serve started letting her down -- she had a success rate of just 40% in the second set -- and she failed to keep her hold on the match. Riske took advantage of the Australian's frustrations and advanced 3-6, 6-2, 6-3.

Riske, unseeded and ranked 55th, saw the opportunity and took it -- being one of those players who almost unfailingly gets everything back and is always there to find a way, slam or slice, to keep the ball in court. Barty said as much afterward, that she had lost to a better player and that Riske's natural comfort on grass allows her to produce a powerful, back-against-the-wall brand of tennis that leaves few gaps to expose. It perhaps explains why Riske is 14-1 in her past 15 matches on the surface.

Riske's comments postmatch were laced with military metaphors -- she talked of how she's a battler and ready for war against Williams. While there is this steely side, she was also full of excitement and emotion as she weighed up what she achieved and what was to come. She remembered her first matches on grass fondly, but if you want a sign of how different their tennis worlds are, then consider that Riske played her first competitive matches on the surface in 2009, by which point Williams had already won Wimbledon twice.

Riske joked about how she wants to live in London someday with her fiancé, Stephen; a move she hopes will come with a membership to the All England Lawn Tennis Club. She brushed off any questions about how Australian analyst Craig O'Shannessy had helped her game, after her coaches picked his brain before she faced Barty.

Then Riske spoke of how touched she was when outgoing Wimbledon chairman Philip Brook remembered her name after her 2010 debut. It finished with her in tears as her mind drifted to the late former Davis Cup captain Paul Hutchins. It was a news conference full of contrasting emotions following a performance of steely resolve. And herein lies the greatest danger to Williams -- this combination of excitement, emotion and focus has the potential to throw unpredictability into the mix. The two have never faced off in a competitive match, but they do know each other.

Williams and Riske teamed up in a 2015 Fed Cup match to play doubles against Italian duo Sara Errani and Flavia Pennetta. They lost in straight sets. It would barely warrant a sentence in Williams' tennis chronicles, but she still remembers Riske's competitiveness and also how she was a fighter on court. "I think she's a great girl, a great person," Williams said of Riske. "She's just kind of a great personality that you kind of gravitate to."

But expect her to give few courtesies when they next meet. Williams is now self-declared pain-free after struggling with a knee injury. Gone are those hours after training or a match where she'd have intense physio to reduce the pain to 50%. Those awkward midmatch moments where she had to tailor her game to meet her own pain threshold are also an unhappy memory now swiped to history.

"I literally can't even tell you how much better I feel," Williams said. "That's a relief. That's a victory in itself, to know that I'm feeling better no matter what. I'm on the right path. I finally found the solution. I can be strong for the rest of the year."

And that should be ominous for the rest of the draw. Williams spent as much time answering questions postmatch about her mixed doubles travails with Andy Murray -- please call them "Murena" rather than "SerAndy" -- as she did about her own form. It's the familiar, the taken-for-granted point of the second week where tennis is expecting another Serena crescendo.

For Riske, Tuesday is an unknown quantity -- her first Grand Slam quarterfinal against one of the world's greatest players. Expect her to throw everything against Williams -- Barty exclaimed as much -- and write her off at your peril. For Williams, it'll be business as usual. And all this as she continues to brush off the rust.