Sinner on Sunday added the US Open to his Australian Open triumph in January.
He swept Taylor Fritz off court in a brutally one-sided final, becoming the first man since Guillermo Vilas in 1977 to win his first two Grand Slam titles in the same season.
That is a feat that eluded Roger Federer, Novak Djokovic, Rafael Nadal as well as Pete Sampras and Andre Agassi.
Two years Sinner's junior, Alcaraz won the French Open and defended his Wimbledon title in 2024 and already has four Grand Slam titles to his name.
"It's a bit different, for sure," Sinner said Sunday when asked to assess the new era.
"It's nice to see new champions. Nice to see new rivalries. I will always have players who are going to make me a better player because there are going to be times where they beat me.
"Then you have to try to find a way how to win against certain players."
The beanpole Italian has six titles this year while Alcaraz has three. Both men have already pocketed 15 titles in total each in their careers.
Alcaraz is making Grand Slam history faster than the 'Big Three' of Federer, Nadal and Djokovic despite a shock second-round exit at the US Open.
None of the three legends managed to win four majors before their 22nd birthday.
Djokovic did not win his fourth Slam until the 2011 US Open when he was 24.
Setting Slam records
Nadal was 22 when he earned his fourth at the French Open in 2008 while Federer was 23 when he collected a fourth major at the 2004 US Open.
Alcaraz could claim a career Grand Slam at the age of 21 if he wins a maiden Australian Open in January next year.
Djokovic remains marooned on 24 Grand Slam titles, a record for a man but still level with Margaret Court in the all-time total.
For the first time since 2017, he will finish a season without a Grand Slam trophy.
Djokovic will be 38 next May and if he were to add another Slam to his collection, he would be the oldest major singles champion, surpassing Ken Rosewall who was just over 37 when he clinched the 1972 Australian Open.
The now-retired Roger Federer was 36 and five months old when he claimed his 20th and last Slam at the 2018 Australian Open.
Nadal will turn 39 in May next year but the injury-plagued Spaniard is on the brink of retirement.
He was two days past his 36th birthday when he won his 22nd major and 14th French Open in 2022.
This year was the first since 2002 that at least one of the Slams had not fallen to a member of the Big Three.
Fritz, playing in his first Slam final at the age of 26, believes the majors are more open than ever.
'Go deep in tournaments'
"I don't think you have to play unbelievable to go deep in tournaments and contend," he said on Sunday.
"You can find yourself a little deeper in the draws, like quarter-finals and stuff, if you just play solid tennis, although I still think to beat the top guys you need to bring your best game."
Both Djokovic and Nadal are expected to return to action in the coming days.
Djokovic is on Davis Cup duty in Belgrade with Serbia in the week ahead while Nadal, who hasn't played since the Olympics, is due to feature in the Laver Cup in Berlin from September 20th.
Both men are likely to face questions over their future plans in a sport they dominated for the greatest part of two decades but for whom the clock is ticking.
