Serena Williams must hope the effort of playing two doubles matches in a matter of hours does not take a heavy toll as she tackles Victoria Azarenka in today's Wimbledon semi-finals.
Together with sister Venus, Williams returned to Court Two yesterday to finish off a rain-delayed second-round clash against Russians Maria Kirilenko and Nadia Petrova, and the pair then played a full match on the same court against fellow American Bethanie Mattek-Sands and India's Sania Mirza.
The Williamses won both and are billed to play doubles again today against Raquel Kops-Jones and Abigail Spears, but only once Serena's rather more important singles clash with world number two Azarenka is out of the way.
The four-time singles champion at Wimbledon, who with Venus has also won the doubles title on four occasions, heads into her match against Azarenka boasting a record of seven wins in eight past meetings with the Belarusian.
Yet 30-year-old Williams has no doubt Azarenka, who won the Australian Open in January, is an opponent to be feared.
"She's playing unbelievable. I think she's played so well this year," Williams said.
"Already having a grand slam under her belt is really great. She did it in such style, so it's not going to be easy."
Williams says she has "absolutely nothing to lose", positioning herself as the underdog.
That might amount to a stab at mind games, but as sixth seed Williams pointed out: "She's had a better year than I have. She's been so successful already.
"Going against a player like that, I feel like she almost has an advantage."
Azarenka is the only semi-finalist yet to have dropped a set, and until a dramatic finale to her last-eight clash with Tamira Paszek, decided on a second-set tie-break on Tuesday night, she had not been pushed at all.
The 22-year-old from Minsk is not flinching as the imposing figure of Williams looms.
"I don't really like to look back in history," she said, "because every time you step on the court it's a new story.
"You kind of write your own history every time.
"I've lost to her most of the time. But I think we played once here only."
That encounter came three years ago, when Williams won for the loss of five games against a teenage Azarenka in the quarter-finals.
"It's going to be a tough match no matter what," Azarenka said. "But that's what you kind of expect to have in the semi-finals. We had good matches. We had bad matches. We'll see."
Germany's Angelique Kerber and Poland's Agnieszka Radwanska go head to head in the opening semi-final on Centre Court, at 1pm.
Radwanska can rise from third to number one in the rankings by carrying off the title, even though this is the first time the 23-year-old has reached a grand slam semi-final.
Kerber is the eighth seed but beat Radwanska at last year's US Open, and went on to reach the semi-finals there.
Kerber said ahead of their rematch: "I know I need to play at my highest level to beat her."