The world number one, looking to lift the Suzanne Lenglen Cup for the third time in four years, started strongly before briefly struggling on Court Philippe Chatrier.
With several sponsors' seats empty in the middle of the afternoon, the Pole picked herself up quickly to end Liu's campaign in brutal fashion.
"It's not easy when you play with the wind and change sides to play against it. I'm happy I raised my level in the second set," said Swiatek, who turned 22 on Wednesday.
"Patience is important, especially on clay."
Swiatek raced to a 3-0 lead on a sunbathed court Philippe Chatrier but she looked too much in a hurry and Liu pulled one of two breaks back as the Pole briefly lost her focus.
Liu levelled for 3-3 but dropped serve again as Swiatek bagged the opening set.
She did not look back, ending her opponent's ordeal on the second match point with a backhand winner down the line.
