List of champions of the 1889 U.S. National Championships tennis event (now known as the US Open). The men's tournament was held from August 27 to September 3 on the outdoor grass courts at the Newport Casino in Newport, Rhode Island. The women's tournament was held from June 11 to June 15 on the outdoor grass courts at the Philadelphia Cricket Club in Philadelphia, Pennsylvania. The men's doubles event was played at the Staten Island Cricket Club in Livingston, Staten Island, New York. It was the 9th U.S. National Championships and the second Grand Slam tournament of the year. The inaugural U.S. Women's National Doubles Championship was held in 1889 and like the women's singles was played at the Philadelphia Cricket Club.:

Finals

Men's singles

🇺🇸 Henry Slocum defeated 🇺🇸 Quincy Shaw 6–3, 6–1, 4–6, 6–2

Women's singles

🇺🇸 Bertha Townsend defeated 🇺🇸 Lida Voorhees 7–5, 6–2

Men's doubles

🇺🇸 Henry Slocum / 🇺🇸 Howard Taylor defeated 🇺🇸 Valentine Hall / 🇺🇸 Oliver Campbell 6–1, 6–3, 6–2

Women's doubles

🇺🇸 Margarette Ballard / 🇺🇸 Bertha Townsend defeated 🇺🇸 Marion Wright / 🇺🇸 Laura Knight 6–0, 6–2