Alcaraz was brilliant as he piled into the French Open quarter-finals for a third straight year, destroying Canadian 21st seed Felix Auger-Aliassime 6-3 6-3 6-1 on Sunday with typical brio to set up a clash with former finalist Tsitsipas, who found it harder to subdue Italy's Matteo Arnaldi 3-6 7-6 (7-4) 6-2 6-2.
But it is what comes next for Tsitsipas that should concern him.
"I've seen a lot of matches lately from Stefanos. I know he's playing great tennis and has a lot of confidence right now. I have the key against him," said Alcaraz.
"I'll try to play the shots that get him in trouble. I'll try to show my best."
Later, the two-time slam-winning Spaniard wouldn't elaborate what that 'key' to beating the No.9 seed Tsitsipas is, shrugging: "I know tactically what I have to do in the match, which I'm not going to say, obviously."
But he pointed out simply and brutally: "The matches that we've played, I won all of them."
Stefanos Tsitsipas shows his delight after winning a fourth-round match against Matteo Arnaldi. (AP PHOTO)
Indeed, Tsitsipas should be very afraid. His head-to-head record against the 21-year-old is won 0, lost 5, with the last three coming on clay during which the Greek has won just one set.
Not that the ever-reflective Tsitsipas sounded too alarmed as he responded: "He (Alcaraz) has said in the past that he likes to play against me ... I hope he likes it a little bit less."
Tsitsipas is still after that elusive first grand slam title, but the 2021 Roland Garros finalist was certainly given an early jolt from Arnaldi, just as Jannik Sinner received from home favourite Corentin Moutet in a lively night match on Chatrier.
Southpaw Moutet, a bearded piano-playing, poetry-writing, occasionally underarm-serving artist of the court, painted a first-set masterpiece, bursting into a 5-0 lead to dumbfound the Australian Open champ.
But, even with the crowd raised to noisy fever pitch, reality inevitably bit after Sinner had lost his first set of the championship, with the Italian, who's still only lost two matches all year, soon stopping the music on the way to reeling off a 2-6 6-3 6-2 6-1 victory.
The volatile Frenchman continued to provide rich entertainment, though, as things began to implode, losing his rag spectacularly when he got called for a foot fault while trying an underarm serve and then trying to break his racquet and failing ignominiously. Â
"He played very, very well the first set, and I had to adjust. He plays different than most of the opponents, he's a lefty too, so I'm happy to be in the next round," said Sinner.
The No.2 seed just got on with business quietly and icily amid the mayhem, watched by his eagled-eyed Australian co-coach Darren Cahill, carving out a win that sets him up for what should be a swashbuckling quarter-final with 10th seed Grigor Dimitrov, who's enjoying a fabulous renaissance at the age of 33.
The Bulgarian fought past Poland's Hubert Hurkacz 7-6 (7-5) 6-4 7-6 (7-3) after picking himself off the clay when he took a tumble that made his hand bleed and required him to be treated on court.
