Andy Murray's much-vaunted returning skills will be tested to breaking point at Wimbledon on Friday while Roger Federer faces a more subtle examination from a man in too much of a hurry to be blinded by reputation.
Murray's semi-final against the resurgent Andy Roddick is one of those irresistible meetings of players with perfectly contrasting strengths.
Murray, aiming to become the first Briton to reach the men's singles final at Wimbledon since Bunny Austin in 1938, has been hailed as one of the best returners of serve on grass. Roddick, the 26-year-old American, has a serve that is a huge weapon on any surface.
Federer's semi-final will test his intelligence as much as his reactions as he takes on Tommy Haas, the 31-year-old German who is basking in the warmth of an unexpected Indian summer.
While Federer aims for his 15th grand slam singles title, an achievement that would take him out on his own ahead of Pete Sampras, Haas is eager to make up for lost time.
The German has come here for once injury-free and he has lit up the championships by mixing classic serve-and-volley with wit and innovation from the back of the court.
Haas let Federer off the hook when they met at the French Open, letting the Swiss come back from two sets and break-point down, and with that heroic tussle still fresh in everyone's mind their meeting on Friday will have added piquancy.
For the home crowd, of course, whatever delights Federer and Haas serve up it will not match their enthusiasm for Murray.
The 22-year-old Scot made life difficult for himself going to five sets against Stanislas Wawrinka under the roof but he made up for it by beating Juan Carlos Ferrero with ruthless efficiency in Wednesday's afternoon sun.
"You know, I think he's one of the best returning guys that there is on a grass court," Ferrero said. "He returns everything, no matter how you serve."
Murray's own serve also looked in good shape and when his game came together in the second set he looked untouchable, rattling off five games in 10 minutes.
It will be harder to conjure that level of dominance against Roddick, a man who has twice reached the final at Wimbledon and is back playing with the sort of indefatigable spirit that made him a U.S. Open champion at the age of 21 in 2003.
Murray has won six of their eight previous matches, including one at Wimbledon in 2006.
Roddick's recent work on his fitness means he is now lighter and stronger, although such a tough work-out against Hewitt will test his powers of recovery to the limit.
"I feel fit and I feel healthy," said Roddick said after serving 43 aces in a 6-3, 6-7, 7-6, 4-6, 6-4 victory over the dogged Australian Lleyton Hewitt in a quarter-final scrap that will live long in the memory.
"I'm in better shape now than I was when I was 24."
Haas, who was once ranked as high as second in the world, is another player who looks better than ever here.
After saving two match points against Marin Cilic in the third round, Haas has gone from strength to strength and reached the semis with a cool victory over world number four Novak Djokovic on Wednesday.
Federer, making his 21st consecutive appearance in a grand slam semi-final, is a step up in class even from Djokovic.
The Swiss reached the last four by dismantling the Ivo Karlovic serving machine in a straight sets victory.
"Against Tommy I have to play a good match from the start," Federer said. "As we saw in Paris, it was brutal.
"Yeah, it's gonna be tough but, you know, I'm happy to be back in another semi-final. The 21st in a row. It's amazing. Means the world to me. Let's see what happens now."