The Serbia international, 23, will battle for the number-one spot at Stamford Bridge alongside Robert Sanchez.
It happens when Edouard Mendy joined al-Ahli and Kepa Arrizabalaga was loaned out to Real Madrid. It's a major step, and joining one of the greatest teams in the world has always been a goal of mine, said Petrovic.
He said, "Today I accomplished that goal, and I'm so happy."
He has signed a seven-year contract with Stamford Bridge that includes a one-year extension option.
Let's hear from Djordje! 🎙️ pic.twitter.com/vy5AhEEPAi
— Chelsea FC (@ChelseaFC) August 26, 2023
Petrovic appeared in 43 MLS games for New England and has two Serbian caps.
Chelsea goalkeeper Marcus Bettinelli is now sidelined with an injury, while 20-year-old Lucas Bergstrom has been on Mauricio Pochettino's bench for the first three Premier League games of the season.
The club has spent more than £323 million on eight players in this transfer window than any other team in Europe, breaking the record for the largest summer spend by any club in the world and surpassing Real Madrid's £292 million in 2019.
Since owner Todd Boehly took over last summer, they have spent more than £850 million in the market.