The top seed, who lost to Novak Djokovic in the French Open quarter-finals last week, was beaten 6-4, 6-7 (3/7), 6-3 by the 170th-ranked Brown.
The 18-year-old looked unbeatable on serve as he eased past Gulbis in straight sets to continue an impressive season in which he has shot to 21st in the world rankings.
Five-time Grand Slam champion Sharapova has been sidelined since February after having surgery on a shoulder problem which has troubled her since 2008.
Sharapova, 32, a five-time Grand Slam champion, has been sidelined since February after having surgery on a shoulder problem which has troubled her since 2008.
French veteran Tsonga thrashed Zverev 6-3, 6-0 and Serbian teenager Kecmanovic came from behind to beat 35-year-old Kohlschreiber 4-6, 7-5, 6-3, before the rain came down and play was suspended on centre court.
Naomi Osaka narrowly retains top spot despite her shock elimination in the third round at Roland Garros.
Austrian Dominic Thiem, whom Nadal beat in Sunday's final, keeps his fourth place behind Switzerland's Roger Federer.
The Spaniard's historic 12th Roland Garros triumph took him to 18 majors, just two behind Federer.
The 33-year-old Spaniard becomes the first player, man or woman, to win the same Slam 12 times after seeing off a brave challenge from a weary Thiem in a repeat of the 2018 final.
Victory on Sunday will move Nadal on to 18 majors, just two behind Federer on the all-time list.
Eighth seed Barty got off to a strong start and never looked back, winning 6-1, 6-3 after only 70 minutes to claim her maiden Grand Slam title.
The 25-year-old Austrian fourth seed downed the world number one 6-2, 3-6, 7-5, 5-7, 7-5 to set up a repeat of last year's final against 11-time winner and defending champion Rafael Nadal.
Djokovic, bidding to become just the second man in history to hold all Grand Slam titles at the same time twice, was trailing 1-4 in the final set and was 40-40 when play was halted.
Austrian fourth seed Thiem led 6-2, 3-6, 3-1 against the world number one when the players left Court Philippe Chatrier.
Swiss maestro Federer slumped to a 6-3, 6-4, 6-2 loss to 11-time French Open champion Nadal in the semifinals on Friday.