Roger Federer has one of the best highs, so when he fails in two strikes on his way to lose his serve in the second half of the meeting with Greek Stefanos Titipas in the semi-finals of the men's tennis season on Saturday; he knew that he may face a difficult day.

The Swiss Maestro, who has won 20 Grand Slam titles, lost 6-3 6-4 to the 21-year-old, who was stunned by his debut.

While Titipas, according to Federer's description, was "hard like nails," the Swiss took one of 12 break opportunities to vanish his hopes of a seventh title in the final.

"I think I crashed after failing two shots in one half, and that didn't happen very long, or maybe at all," the 38-year-old told reporters. "It was difficult. This is something you can't train or prepare for. That's hard. They are not ready or not ready for high strikes and all these things. "

Despite failing to do what he did on Thursday when he beat Novak Djokovic, Federer did not perform poorly.

If he had taken advantage of his chances, the situation might have been different. The ninth game was crucial in the first set, when the two players exchanged for 13 minutes and Federer had six chances to break the serve, before the fierce Titipas settled it for him.

Federer responded by breaking his opponent early in the second set, but Titipas refused to retreat to his second victory over Federer this year.

Big Three
Titipas's win came to bid farewell to the last three big players, following Djokovic and Rafael Nadal.

With Alexander Zverev, 22, facing Domenech Tim, 26, in the other semi-final, it is yet another sign that the old guard is under attack ever stronger or perhaps not.

"I think they have proved themselves this year by qualifying for the final, and now maybe at least one will reach the final, or Alexander will repeat what he did last year," Federer said.

"But I look at who finished the year at the top of the rankings and who was the number one in the world all year, it is crazy that he is always one of us."

"But we are not getting younger; so opportunities increase not because of our decline but because they are getting better."

Some will not doubt that Titipas' attacking style will get Federer's blessing, and the Swiss player praised his young rival, who has stunned the world rankings, to be among the top 10.

"I have to praise him for putting pressure on me and forcing me not to do the performance I wanted today. His moves have always been fierce, he will attack any shot, and I think he's doing it very well. He's one of the best players in doing that," Federer said.

Despite winning four titles this year and taking his tally to 104 titles, Federer failed to boost his record in the Grand Slam.

"I have to keep playing at this level, as I did this year, then I will get some chances," he said.

Titipas managed to win with his bold strokes, regular progress on the net and a strong serve to give him a lot of praise, but at the same time he is aware that Federer's fans find it hard to accept his victory.

"I hope I like them when I play because I feel like I have a lot of things I can give to tennis," he said. "I hope to see one day a big fan base coming to me for me like Roger, because these fans are the army for him. And of course I need that; I need an army like this.

What worries his fellow young players, who will definitely compete with Titipas for major titles, is his ability to shine during difficult times, as he showed when he lost to Rafael Nadal in a match he did not need to win, though he fought for about three hours last Friday.