Sabalenka replaces Serena in top 10 after Linz title
The 22-year-old Sabalenka finished the season in style with a straight-sets victory over her doubles partner Elise Mertens in Sunday's final in Austria.
She traded places with Williams, who dropped one spot to 11th and hasn't played since pulling out of the French Open with an Achilles injury.
Ashleigh Barty remains clear at the top despite skipping both the US and French Opens following the season's resumption after the coronavirus shutdown. Her last match was at the Qatar Open in February.
Belgian Mertens moved up one place to 20th, climbing above last year's Roland Garros runner-up Marketa Vondrousova.