That's not forgotten, is it? McEnroe couldn't cope with Lendl's power baseline game in 1981-1982 and January 1983, especially the big forehand (for the time). Connors, on the other hand, seemed to thrive on Lendl's power game in the same time frame in most of their matches. Lendl learned over time against Connors to hit the ball with less pace, more slice, move Connors around etc.
McEnroe turned it around slowly against Lendl in 1983, after getting a prep talk from Don Budge. Budge told McEnroe to stop letting Lendl dictate the rallies, to use the serve and volley tactic a lot more and be aggressive off the ground. This turned the rivalry around from spring of 1983 to summer of 1985, with McEnroe winning the vast majority of matches against Lendl. Lendl did have to learn how to get the proper edge over McEnroe all over again, and the 1985 US Open final was the big turning point. Lendl's fitness was a big factor in my opinion, which had been a few years in the making.