Through the first week of the season's final Grand Slam, the world number one has been putting in routine shifts and has dropped only one set en route to the last eight.
But the second week is the business end of a Grand Slam when the draw has thinned and serious contenders surfaced.
In Alcaraz's rear view mirror are relative unknowns, like Arnaldi and Dominik Koepfer (29), but ahead of him lurk familiar danger men such as Daniil Medvedev (27), Jannik Sinner (22) and Andrey Rublev (25).
Alcaraz has not shown his best yet on the New York hardcourts but like a hot Wall Street stock is trending in the right direction.
There have been a few hiccups and lapses but his raw talent, power and a repertoire of weapons make him the man to beat and on track for another showdown with arch rival Novak Djokovic (36).
Under a closed roof on Arthur Ashe Stadium, Alcaraz was solid from start against a man who was playing in the Flushing Meadows main draw for the first time.
It took a few games for Alcaraz to size up his opponent but once the Spaniard did, it was pretty much one way traffic.
Alcaraz took charge with a break for a 4-2 lead in the first set and then broke again at the start of the second to find himself 2-0 up.
The feisty Italian would have his moment in the third set, breaking Alcaraz at 2-1 but the Spaniard would immediately break back and then again to seal victory.
Later Arnaldi confirmed what most already knew - he could see no holes in Alcaraz's game.
"(I) try to not let him find weakness to my game," said Alcaraz. "I try to put him to the limit every time that I can in every match, against every opponent.
"I try to put my own game, try to put my style on the match.
"I'm happy that he said that because I'm doing great things on the court."
It has been rare to catch Alcaraz without a smile whether on court, television or mingling with fans signing autographs.
For now everything is going according to plan and Alcaraz, without a hint of bravado, rated his performance so far as great.
"Honestly, I've played great matches with a great level, high quality," he said. "I hope to keep going like this.
"For me, nothing else matters than playing my level and be happy with the level that I'm playing on court.
"That's the only thing I care about right now.
"All the pressure that people put on you, on the defending champions, I just delete it and focus on my own game."
Alcaraz will next face either Italian sixth seed Sinner or 12th seeded German Alexander Zverev (26).
