Kuznetsova currently sits at No.153 in the world rankings after periods on the sidelines, but made the most of her wildcard in Cincinnati to get past the Australian world No.2.
Despite slipping to 2-0 down in the opener, the two-time grand slam champion clicked into gear spectacularly and reeled off eight consecutive games, a forehand return winner on break point to go 5-2 up a particular highlight.
Barty belatedly held for 1-2 in the second to stop the rot but would never another good look at her opponent's serve. Indeed, Kuznetsova avoided giving up break point opportunities in any of her last eight service games.
The result prevented Barty from returning to No.1 in the WTA rankings after Osaka was forced to withdraw with a knee injury in the quarter-finals.
Madison Keys sealed a place in her first hard court final since the 2017 US Open with a 7-5 6-4 win that included 41 winners over compatriot Sofia Kenin, and will meet Kuznetsova in the decider.
Kenin saved set point in the opener against Keys before battling back from 5-2 down to 5-5, only for the world No.16 to claim back-to-back games and avert a tiebreak at the WTA Premier event.
Keys was twice a break down in the second set but combined grit with blistering attacking play to down Kenin, avenging a three-set loss in Rome earlier this year.