The 1970 US Open was a tennis tournament that took place on the outdoor grass courts at the West Side Tennis Club in Forest Hills, Queens, in New York City, United States.

It was the 90th staging of the US Open, and the fourth Grand Slam tennis event of 1970.

The 1970 US Open was the first tournament to introduce a final set tie-break in a Grand Slam.

It differed from the current tie-break scoring in that it was won by the first player to reach five points with a sudden death at 4-4.

A red flag would be put up by the umpire's seat to draw fan attention to the tiebreaker in progress.