Krejcikova, ranked 33 in the world, defeated America's Sloane Stephens, the 2018 runner-up in Paris, 6-2, 6-0 to record a ninth successive win on the tour.
For the first time since Wimbledon in June 2017, a tournament will have the entire Big Four in the field: Roger Federer, Rafael Nadal, Novak Djokovic and Andy Murray.
The 36-year-old Serena now cannot meet a top 32 player until the semi-finals after the scattering of the seeds this week.
Sloane Stephens became Wimbledon's first big-name casualty this year as the world number four crashed to a shock 6-1, 6-3 defeat against Donna Vekic.
American Sloane Stephens had cause for a double celebration after beating Germany's Angelique Kerber 6-1, 6-2 to reach the WTA Miami Open semi-finals.
The US Open tournament stayed up to the hype surrounding it with Rafael Nadal and Sloane Stephens claiming the title.
Sloane Stephens, the world number 83, raced to a 6-3, 6-0 victory over 15th seeded Madison Keys in just over an hour.
US Open champion Sloane Stephens made her best prior Grand Slam run to the 2013 Australian Open semi-finals.
Keys, the 15th seed, was trounced 6-3, 6-0 by world number 83 Stephens in a one-sided final that lasted just over an hour.
Sloane Stephens won her first Grand Slam title on Saturday, beating fellow American Madison Keys 6-3, 6-0 in the final.
Sloane Stephens admitted to feel nervous the night before the match, saying she was searching for things to do.
After being off tour for 11 months, Stephens easily beat Madison Keys 6-3, 6-0 in the first Grand Slam final for both.