In a matchup of the only two previous Wimbledon champions remaining in the women's draw, Williams saved a set point when trailing 5-4 in the second and then broke Kvitova in the next game.
She served out the match with the help of three aces and a service winner.
Williams broke once in each set and finished with 13 aces and 27 winners overall.
Williams also beat Kvitova in the 2010 semifinals en route to her fourth Wimbledon title.
