Wikipedia[1]: Swissair "introduced it into service on October 10, 1980"; Swissair's fleet history lists it as "First operator of F.100 and MD81 (DC9-81) in 1980".
Swissair, launch customer of the McDonnell Douglas MD-80, put its first MD-81 into service on 10 October 1980, a month after taking delivery of the first aircraft on 13 September 1980.