After holding serve to open set two, a Williams forehand down the line return winner at 15-40 put the American ahead 2-0.
A forehand down the line winner on her serve at 40-0 sent Williams ahead 6-0, 3-0 after only 45 minutes of play.
After three Williams groundstrokes hit long and a Sharapova crosscourt backhand winner, the Russian would take her lone game of the day to pull within 3-1 in set two.
With Williams serving up a break still, Sharapova held two break point chances. However both were soon erased by Williams: the first break point with a Williams swing forehand volley down the line winner and the second with a Williams crosscourt backhand winner.
And with Sharapova constantly on the run at the baseline, chasing the deep angles and powerful down the line groundstrokes from Williams, the Russian would net a crosscourt backhand to fall further behind in set two 4-1.
In her final service game, Sharapova quickly trailed 0-40 before dropping serve to trail 1-5.
In the final game of the match, a Sharapova backhand down the line winner put her ahead 15-0 before a Williams crosscourt backhand winner put the American ahead 30-15.
Two consecutive aces from Williams; number nine and ten both down the tee would end the match.
Serena Williams could win her second gold medal of the week in Sunday’s women’s doubles with her sister Venus Williams should the duo win their semifinal round match later today.
Venus Williams also finished as the Olympic singles gold medalist in 2000 at Sydney, Australia.