The Russian sixth seed and two-time grand slam champion claimed her first WTA Tour title since August 2010 with a 6-3 4-6 6-4 victory in the decider in Washington.
Kuznetsova, looking fit and motivated, grabbed her 14th title as she ended her long wait when Nara sent a forehand long on championship point.
The 2004 US Open champion and 2009 French Open winner - the powerful Kuznetsova is in fine form heading into the year's final grand slam later in August.
In a tense final, which lasted two hours and 16 minutes, Kuznetsova mixed 32 winners with 39 unforced errors.
Japan's Nara kept her unforced errors to just 29 but there were also only 25 winners.
Kuznetsova broke three times in the first set before Nara started taking her opportunities in the second to level the match.
Nara looked the more likely to break in the decider as she put Kuznetsova under pressure in the seventh and ninth games.
But failing to claim the break in a 15-point ninth game would be costly as the 29-year-old broke to 15 in the next to clinch the title.