Iga Swiatek took home the match's first game in its own serve and then immediately broke Kasatkina's serve until 2-0.
Kasatkina responded, however, by both breaking Swiatek's serve and then serving the next game to 2-2.
Then, however, was the fun end for the 25-year-old Russian, who was in his first grand slam semifinal.
Swiatek - who turned 21 as late as Tuesday - took home four straight games and the set with 6-2.
In the second set, Kasatkina equalized to 1-1 - before Swiatek increased the pace again and was able to serve the match home after only one hour and four minutes of play.
If Iga Swiatek goes all the way to her second title at Roland Garros - the first, which is her only grand slam title, she took in 2020 - she will have won 35 straight games, which in that case would be a touch of Venus Williams' listing from 2000 as the best victory suite of the 2000s.
However, up to Martina Navratilova's 74 straight victories from 1984, there is a difference.
In the second semifinal, the 18th-seeded American super talent Coco Gauff, 18, will face the Italian Martina Trevisan.
The start of the ladies' tournament offered a real star fall, where seven of the ten best ranked players went out in the first or second round.