The 14th-seeded Haddad Maia, whose career has been hampered by injuries and a 10-month doping ban, had played four consecutive three-set matches to get to the semi-finals.
Swiatek's previous clashes had lasted a little over an hour each, while Haddad Maia had spent nearly 13 hours on court.
She got a second break for 4-2 when Haddad Maia netted a drop shot attempt and sealed the set with another break.
It seemed Swiatek would stroll through the second set, but Haddad Maier, the first Brazilian woman to reach the last four at major since 1968, had other ideas.
With two big first serves, Swiatek saved them and staved off another before holding, forcing Haddad Maia to serve to stay in the match.
Persons:
Iga Swiatek, Beatriz Haddad Maia, Haddad Maia, Czech Karolina Muchova, Swiatek, Suzanne Lenglen, Philippe Chatrier, Haddad Maier, Julien Pretot, Pritha Sarkar, Ed Osmond
Organizations:
Czech, Thomson
Locations:
Belarus, Polish