You can't measure it on the Centre Court speed gun, but in a Wimbledon quarter-final, especially one against Serena Williams that goes to a third set, your strength of mind is just as important as your strength of shot.
As the daughter of a former secret service agent and FBI investigator, Alison Riske is hardly a soft touch on these lawns. For all her mental hardness and hustle, the unseeded American ran smack into arguably the most competitive tennis player of all time, a woman celebrated for her bloody-minded refusal to yield on the Centre Court grass.
When Riske went an early break up in the third set, it looked as though she had every chance of coming from a set down for a fourth time in The Championships, for what would have been her greatest win of all.
But, in the end, it was Williams - who by then had arranged her hair into a bun, perhaps signalling that it was time to get serious - who prevailed 6-4, 4-6, 6-3, putting the 37-year-old just two more matches from equalling Margaret Court's all-time record of 24 Grand Slam singles titles. As Williams put it, she was "playing hard" against this first-time quarter-finalist.
The very year that the umpires at Wimbledon drop the 'Miss' and 'Mrs' when announcing the score, there has been much interest in Riske's marital status, ahead of her wedding the weekend after next. Riske has been the very opposite of a bridezilla this Fortnight, with her focus very much on her tennis, instead of her wedding planning, and she took it to Williams on Centre Court in a spirited, pulsating match that lasted a minute over two hours.
Playing against Williams on this rectangle of grass, with a place in the Wimbledon semi-finals as the prize, is an experience that would unnerve most. But not Riske. Only once did she look at all disorientated, which was when she lost track of the score midway through the opening set and started to walk towards her chair, thinking that game was over. Easily done. The rest of the time, Riske showed great poise in the biggest occasion of her tennis life.
In the politest possible way - with no hint of animosity - there had been plenty of fighting talk ahead of their first meeting. "I'm ready for a war," Riske had suggested, while Williams had said of her opponent: "She's a fighter on the court." Anyone who came back from a set down in three of her first four matches, including against the Australian top seed Ashleigh Barty in the fourth round, isn't lacking for mental fortitude.
Riske had played more than nine hours of tennis to make the last eight, which was more than any other quarter-finalist. By contrast, Williams had spent less time on court than anyone else in that octet, with a little over five hours of competitive play from her first four matches.
While outside the 32 seeds, Riske feels at ease on a grass court, and going into this quarter-final she had won 14 of her 15 matches on the surface this season, with that success bringing her a WTA title in the Netherlands last month. Certainly, she had played much more on grass this year than Williams, who followed her usual routine of skipping all warm-up tournaments.
While Riske twice led by a break, it was Williams who took the opening set. Would Riske come back from a set down once again? She certainly didn't disappear from view, breaking for 5-4 in the second set and then serving it out to love.
While Riske broke in the opening game of the third set, Williams immediately had parity. They exchanged a couple more breaks, before Williams went 5-3 ahead when Riske double faulted on break point. Williams completed her win with an ace, a great roar and then a smile.
