The 1973 Union Trust Classic, also known as the Washington Indoor, was a men's tennis tournament played on indoor carpet courts at the Four Seasons Tennis Club in Merrifield, Virginia in the United States that was part of Group B of the 1973 World Championship Tennis circuit.

It was the second edition of the tournament and was held from March 19 through March 25, 1973.

Unseeded Tom Okker won the singles title and earned $10,000 first-prize money after his opponent in the final, fifth-seeded Arthur Ashe, failed to convert two matchpoints in the final set.

[3][4][5][6] Tom Okker defeated Arthur Ashe 6–3, 6–7(4–7), 7–6(7–3) Tom Okker / Marty Riessen defeated Arthur Ashe / Roscoe Tanner 4–6, 7–6, 6–2