The 26-year-old jumped above Poland's French Open champion Iga Swiatek thanks to year-end adjustments in the standings.
Aryna Sabalenka said Tuesday that she wants to cap off a stellar year by returning to the top of the world rankings.
With Roger Federer retired and Rafael Nadal struggling to get back on court due to injuries, Novak Djokovic was the last man of that golden generation standing at Flushing Meadows, but the Serb crashed out in the third round to Australian Alexei Popyrin.
"I'm speechless right now. So many times I thought I was so close to get the US Open title. It has always been a dream of mine and finally I got this beautiful trophy," said Sabalenka.
Sabalenka sent down 34 winners to the 13 of the 23-year-old American in the tie.
Aryna Sabalenka detailed her current tennis philosophy on Tuesday, with the three-time Cincinnati Masters semi-finalist revealing she's quick to forget about her losses.
Osaka returned to the tour this year after 15 months of maternity leave for her daughter who turns one on Tuesday.
Russian teenager Mirra Andreeva became the youngest Grand Slam semi-finalist since 1997 with a shock victory over second seed Aryna Sabalenka, who was struggling with an apparent illness, at the French Open on Wednesday.
The current Australian Open champion arrived at Roland Garros as a top contender.
Coming back from 1-3 down in the decider and saving three match points in total, Swiatek claimed a 7-5, 4-6, 7-6 (9/7) victory to secure the Madrid Open trophy for the first time.
"Today was the test of fire, no discomfort, feeling spectacular... from here, we'll be getting better."
Defending Madrid Open champions Carlos Alcaraz and Aryna Sabalenka both triumphed in their opening clashes in the Spanish capital on Friday to reach the third round.
Top seed Swiatek, the 2022 and 2023 champion at the German clay-court tournament, saw off former US Open champion Raducanu 7-6 (7/2), 6-3.
"Konstantin's death is an unthinkable tragedy," Sabalenka said in a statement released by her agent.
Sabalenka's partner, Belarusian former NHL ice hockey player Konstantin Koltsov, 42, died late Monday after jumping from the balcony of a room in an upmarket resort in Miami, police said.
Konstantin Koltsov, the Belarusian former pro ice hockey player and boyfriend of tennis player Aryna Sabalenka, has died at the age of 42, Russian club Salavat Yulaev said in a statement on Tuesday.
An authoritative Aryna Sabalenka blew China's Zheng Qinwen off court on Saturday to successfully defend her Australian Open title -- the first woman to do so in more than a decade.
The Belarusian world number two has yet to drop a set in Melbourne this year
Aryna Sabalenka has blown all-comers off court on her march to the final of the Australian Open and China's Zheng Qinwen will need to produce something extraordinary to deprive her of back-to-back titles on Rod Laver Arena on Saturday.