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.
Second seed Aryna Sabalenka recovered from a set down to beat France's Varvara Gracheva 2-6, 7-5, 6-2 and reach the last 32 at Wimbledon on Friday.
Unseeded Karolina Muchova saved a match point before battling past second seed Aryna Sabalenka 7-6(5) 6-7(5) 7-5 on Thursday to reach the French Open final in thrilling fashion and end the Belarusian's dream of becoming world number one.
Elina Svitolina accused Aryna Sabalenka of deliberately "inflaming" the tense stand-off between Ukraine and Belarus players at the French Open on Tuesday by staring her down at the net.
World number two Aryna Sabalenka of Belarus powered past Ukraine's Elina Svitolina 6-4 6-4 in a highly anticipated clash on Tuesday to reach the French Open semi-finals.
Aryna Sabalenka beat 2018 finalist Sloane Stephens 7-6 (7/5), 6-4 in a topsy-turvy encounter in the night session -- the first women's match to feature in the primetime slot this year.
The Belarusian second seed is yet to drop a set in the tournament after a comfortable 6-2, 6-2 win against the world number 82.
World number two Aryna Sabalenka cruised into the French Open third round on Wednesday with a straight-sets win over fellow Belarusian Iryna Shymanovich.
The big-hitting Belarusian gained revenge for defeat by her Polish rival in the Stuttgart final a fortnight ago with a thrilling triumph to end Swiatek's nine-match winning streak ahead of her French Open defence
Rybakina, playing in her first WTA 1000 final, saved three set points in the opening frame and was never really tested in the second where she cruised to a victory that will send her to a career-high seventh in the rankings
The Australian Open set a Grand Slam attendance record with more than 900,000 spectators visiting over three weeks, organisers said on Tuesday, despite the absence of some big-name players and schedule disruptions due to rain.