1991 Thriftway ATP Championships

The 1991 Cincinnati Open, known by the corporate title of the Thriftway ATP Championships was a tennis tournament played on outdoor clay courts. It was the 90th edition of the tournament and was part of the ATP Super 9 of the 1991 ATP Tour It took place in Mason, Ohio, United States, from August 5 through August 11, 1991.

The tournament had previously appeared on the Tier III of the WTA Tour but no event was held from 1989 to 2003.

Singles
🇫🇷 Guy Forget defeated 🇺🇸 Pete Sampras, 2–6, 7–6(7–4), 6–4
 * It was Guy Forget's 3rd title of the year and his 6th overall. It was his 1st Masters title.

Doubles
🇺🇸 Ken Flach / 🇺🇸 Robert Seguso defeated 🇨🇦 Grant Connell / 🇨🇦 Glenn Michibata 6–7, 6–4, 7–5