Both aged 20, born six days apart, the young guns who will be contesting the first men's Wimbledon quarter-final involving two players aged 21 or under in the professional era.
Spaniard Alcaraz is the 'younger' of the two former junior rivals and doubles partners but has leapt ahead with his meteoric rise to the top of the world rankings and landmark triumph at last year's U.S. Open.
Denmark's Rune, the world number six, has shown at Wimbledon, however, that he is not too far behind, thrilling crowds with his eye-catching shots and on-court charisma.
With the retirement last year of Roger Federer and Rafa Nadal soon to follow, men's record 23-time Grand Slam champion Novak Djokovic is last man standing of tennis's golden triangle.
A potential Wimbledon final between defending champion Djokovic and Alcaraz is the talk of the town, but with a 16-year age gap it is likely to be an intense but short-term rivalry.
That is why there is so much excitement brewing about Wednesday's Alcaraz and Rune quarter-finals showdown - it could well be a juicy foretaste of things to come.
"I believe you need rivalries. You think about how much better the men have got because they've played each other so often. It's insane," John McEnroe, whose duels with Bjorn Borg became part of tennis folklore, said earlier this year.
"You're hoping, as Djokovic and Nadal wind down, you're hoping Alcaraz and Rune in particular step up and have a great rivalry because all sports need it."
Alcaraz and Rune are one apiece with the Spaniard winning at the ATP's Next Gen Finals in 2021 over a short format and Rune at the 2022 Paris Masters when Alcaraz retired injured.
So Wednesday's best-of-five-set clash feels like a lift-off moment for their fledgling rivalry and the first proper chance for fans to feast on the myriad range of fearless shot-making they bring to the court.
"I'm really excited about this match. We shared a lot of great moments. We played together since we were 12 years old," top seed Alcaraz said after his fourth-round win over Italian Matteo Berrettini on Monday.
"He has a lot of passion. He loves the game. He's a really competitive guy."
Rune's laid-back demeanour on court is quite a contrast to Alcaraz's hyper-active focus, but his fighting spirit was unquestionable as he saved match points during a thrilling win against Alejandro Davidovich Fokina in the third round.
He said he had envisaged a quarter-final collision with his old buddy Alcaraz since the draw was made.
"I'm really looking forward to that match. I couldn't really afford to look at it because there were so many matches before this would eventually happen," Rune told reporters.
"Now we're here so I'm really pumped and excited for it."
