Novak Djokovic must have been relieved to have given his weary legs a relatively quick workout last night, with a 6-1 4-6 6-1 6-4 victory against Czech fifth seed Tomas Berdych in the Australian Open quarter-finals.
The world No 1, bidding to become the first man to win three successive Australian Open titles since the game went professional, was exhausted from a marathon five-set, five-hour clash against Stanislas Wawrinka on Sunday.
Berdych appeared quietly confident. He had entered the tournament with his highest Grand Slam seeding of five and had barely been pushed throughout his first four rounds.
His longest match had been 2h 44m against Kevin Anderson and that was really only extended by a marathon third-set tiebreak that he clinched 15-13.
If ever there was a time for him to claim his second career win over the Serb and first since their 2010 Wimbledon semi-final, it was at Melbourne Park yesterday.
Djokovic had different ideas.
He hid any signs of fatigue, bounced on his toes throughout, and effortlessly scrambled and slid across court to advance to a semi-final against Spain's David Ferrer.
"Obviously, it's not easy to always be at your 100% fitness," Djokovic said following the two-and-a-half-hour win.
"But after a five-hour match two days ago, I was quite convinced I could recover for this one. I felt good enough to go another five hours, but I definitely wasn't thinking about it.
"I tried to get the work done as fast and efficiently as possible.
"I was very happy with the way I started the match. Very aggressive out there, going for my shots, which wasn't the case against Wawrinka.
"So it's a good improvement and very encouraging for my next match."
It was obvious Berdych knew he had missed an opportunity.
The tall Czech cut a despondent figure in his post-match media conference, looking down constantly and defensively crossing his arms, as he picked at his fingernails.
They were signs of a man looking for answers. How could he have let the chance go, particularly when he felt the Serb had not played as well as he could?
"The only thing I can say that I played him many matches," Berdych said. "Actually, I seen him play way better.
"He's played really good today, but the matches before he played much, much better.
"It was quite kind of a chance for me, but I didn't come up with my best game and that's what was deciding today."
Berdych felt he had played at about "75%" of his ability and that his ball striking from the beginning of the first set had been off.
"I was really quite not hitting the clean balls. That's very big problem, because the ball doesn't have a speed, it's not long enough, then it was quite easy for him.
"I was not able to be aggressive enough. That's it."