The 11th-ranked Andreeva stunned the Belarusian 2-6 6-4 6-3 in Sunday's final at Indian Wells in the California desert.
Andreeva improved to 19-3 this season - the most wins on the WTA Tour - and collected her second Masters 1000 title of 2025.
The other came in Dubai in February, which earned her a top-10 ranking for the first time. Andreeva will return to that upper tier in the next WTA rankings.
Revisiting a theme from her Dubai victory speech that referred to something rapper Snoop Dogg said when he received a star on the Hollywood Walk of Fame, Andreeva told the crowd: "I would again like to thank myself for fighting until the end and for always believing in me and for never quitting."
After dropping the first set against three-time grand slam title winner Sabalenka, Andreeva put her body into the wind-up after grabbing a ball, then angrily smacked it towards the stands.
Wearing training tape on her right shoulder, Andreeva played much better in the second set, particularly on serve, while compiling a 17-7 edge in winners. Soon enough, that set belonged to her when she hit an ace to hold at love for the first time all day.
The teenager started the deciding set in the best way possible, breaking the big-serving Sabalenka at love. Andreeva took a 1-0 lead in the third with a passing shot that Sabalenka could barely even get her racquet on.
Soon, Andreeva's lead was 4-2 and she never faltered. She ended the match with one last forehand winner, then dropped to her knees and covered her face with both hands.
"Congrats on an incredible run," Sabalenka said during the trophy ceremony. "Great tournament. Great tennis."
This was Andreeva's fifth consecutive victory over a top-10 opponent, and Andreeva is now 9-5 against players ranked that high since the start of 2024. That includes two victories each over Sabalenka and No.2 Iga Swiatek, the five-time major champion who lost to Andreeva in the semi-finals at Indian Wells.
Andreeva is the first player under age 18 to beat the women ranked No.1 and No.2 at the same WTA tournament since Williams defeated Lindsay Davenport and Martina Hingis at the 1999 US Open.
The Russian is also the youngest to win a WTA trophy by defeating the woman ranked No.1 in a final since Maria Sharapova beat Davenport at Tokyo in 2005.
