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 Cincinnati, Ohio, USA, from August 12 through August 19 1991.
The tournament had previously appeared on the Tier III of the WTA Tour but no event was held from 1989 to 2003.
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.
Ken Flach / Robert Seguso defeated Grant Connell / Glenn Michibata 6–7, 6–4, 7–5