At a US Open unlike any other, Emma Raducanu created a first in the history of professional tennis and booked a date with Leylah Fernandez in a landmark women's singles final.

Raducanu, 18, defeated Maria Sakkari, 6-1, 6-4, in the second women's semifinal Thursday night in New York. She will face Fernandez, 19, in Saturday afternoon's women's championship. Two teenagers will compete for a first major singles championship, marking the first all-teenage final at a major tournament since Serena Williams (17) defeated Martina Hingis (18) in the 1999 US Open women's final.

As historic as this moment is — and as much of a blockbuster event it will be for women's tennis, which is always looking for telegenic and charismatic new stars with Serena Williams on the last legs of her iconic career — it is magnified a million times over by a mind-blowing fact attached to Raducanu's victory.

Both women are teenagers who have stunned the tennis world by making this final, so it is easy to think they are writing parallel stories, and to a certain undeniable extent, that's true. Yet, while Fernandez's run is remarkable, phenomenal and every other superlative one can imagine, Raducanu's surge to Saturday's final contains several measures of extra historical weight.

The Open Era of professional tennis began in 1968, when the four major tournaments — previously played by amateurs — agreed to welcome professional players to their tournaments, hence the term “Open tennis.” The sport, including the US Open, opened its doors to the pros, who had spent the previous decades barnstorming across the world to play for modest cash prizes in basketball gymnasiums, hockey rinks, and any other facility willing to remake itself into a tennis arena for a few days.

In the 53 years since the beginning of the Open Era in 1968, a qualifier had never reached the final of a major tournament. Qualifiers have to win three matches before the 128-player, seven-round main draw of a major tournament begins. At this US Open, Emma Raducanu became the first qualifier in the history of tennis to make a major final in the Open Era.

Raducanu has won nine matches over three weeks to make Saturday's final, an entirely unprecedented achievement in tennis. Nadia Podoroska of Argentina made the semifinals of last year's French Open as a qualifier, and a few other qualifiers had made semifinals before, but Raducanu is the first to go all the way to the final.

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Get this, too: Saturday's US Open women's final has two players whose COMBINED ages aren't as great as the greatest women's tennis player ever:

One more astounding fact about Saturday at the US Open:

There will be history made on Saturday at the US Open with a first-time major champion as a teenager. More than that, Raducanu — ranked No. 150 — and No. 73 Fernandez will create one of the lowest average rankings (112) for a major final in the history of tennis.

This isn't just two teenagers playing for a major championship; this is tennis history on a scale we have literally never seen before in several different ways. The 2021 US Open has been one for the history books. Saturday, Emma Raducanu and Leylah Fernandez will play for a moment the winner will never forget.