They have the scoreline for the McEnroe/Borg match on Tennis Warehouse: 6-3 2-6 6-4
A list of some special events in which Mac reached at least the final (at least, a span of 4 days):
Dec. 12-18 1977 Nassau Bahamas Tennis Championships: lost to Cliff Richey 5-7 6-4 3-6
Nov. 26-29 1979 Milan Masters Brooklyn Chewing Gum: lost to Björn Borg 6-1 1-6 4-6
May 14-18 1980 Kobe Gunze World Tennis: defeated Victor Amaya 6/2 6/3
May 31-Jun. 5 1982 Manchester GMC Mobens Kitchens: defeated Russell Simpson 6-3 6-7 10-8
Sep. 13-16 1990 Palo Alto California Tennis Challenge: defeated Paul Annacone 3-6 6-4 6-2
Are some of these, Challengers? (you never know !
)