here are some more stats
Cash won 70 of 93 pts on 1st serve(75%)
He won 36 of 70 on 2nd serve(51%)
13 of the 50 return errors he drew were on 2nd serve
1 of his 9 aces was a 2nd serve
He made 1st serves of 5 of the 10 break points he faced(including down match point at 4-5 in the 5th)
He was 95 of 150 at net(63%)
Lendl won 69 of 86 pts on 1st serve(80%)
He won 43 of 76 on 2nd serve(56.5%)
14 of the 44 return errors he drew were on 2nd serve
He made 1st serves on 2 of the 10 break points he faced
He was 11 of 14 at net
I had never heard about any kind of controversy associated with the match and its result; I had always simply heard that it was a great match. But Cash may have been cheated of an ace that would have given him a second match point, on his serve, at 6-5 in the fifth. He was close to being enraged when his hard serve down the middle was called wide. He went on to lose the game on a rare miss off his backhand volley, a stroke that also failed him once during the tiebreak and again on the last point of the match. He was clearly still thinking about the call. He had shouted at the center service linesman upon losing his serve, clearly blaming the man for losing his chance to win.
CBS did not replay the serve, so it’s not easy to tell. But slowing it down by 7x on my DVD, the serve does appear like it could have landed wide. So I don’t think you can say that Cash was truly robbed of the match; the call was too close to say that. Even if he had been, he indisputably let his emotions get the better of him, and could not get the call out of his mind. He seemed afterwards no longer to be in the same efficient and deadly state of mind.
rewatching this again, I was struck by how many bad calls there were throughout the match(you could hear Cash saying something to the umpire as CBS went to commercial at 4-3 in the 5th, after Cash lost a point in which Lendl looked to hit long. Lendl gave Cash an ace early in the 4th set even though cyclops went off. later in the 4th cyclops didn't go off on a Cash serve so Cash got credited with an ace even though the serve was clearly long but the umpire didn't call it - Lendl did tell him that when it was beyond the range of cyclops its his job to call it)
By the time of Cash being 'robbed' of that ace, I imagine he was a bit on edge by the many questionable calls that both players had received & probably thought any close call was the wrong one at that point. The umpire didn't overrule once in this match.