Williams has now knocked out two Americans in the defence of her Flushing Meadows title, and will have to overcome another in the third round in the form of Varvara Lepchenko.
The outlook appeared bleak for world number 81 King from the outset as she saw he serve broken in the opening game, but she took the next to a break point only to see Williams extend her advantage.
King edged the third on her own serve to bring the scores to 2-1, but that proved to be her final contribution to the scoreboard as Williams stepped up a gear.
The 25-year-old forced a break point in the opening game of the second set, but never subsequently looked capable of overcoming her more illustrious opponent.
Williams' power and class told as she managed to dispatch 86 per cent of points on her first serve in the second set, compared to King's 20 per cent.
King was brushed aside in just 56 minutes, with Williams taking a step closer to her 18th grand slam crown.
The reigning champion will now come up against Lepchenko, who defeated Mona Barthel on Thursday.