del Potro match was miles above the Kyrgios match. But people want to see the next big thing, so I won´t argue (more than I already did).
You need to put things into context. The first six games of the first set were played at a very high level. Break points being saved by both players with 90 mph winners touching the line. Nadal was stepping in on the court and making his cross court strokes fly. Stroke by stroke, that phase of the match was light years above the Federer Kyrgios semi, full of crap rallies, UFE´s from Kyrgios and a few stupid mistakes by Federer (unneeded ones). I am sure people will scream in reply (and I don´t care), because the semi was surely tense and very interesting to see. But shot for shot... go and see a rerun on youtube. Start counting the ugly misses. You will give up pretty soon.
So, considering the level that the final match started, it was only natural that one player would start to make more mistakes. Federer needed a higher level of play to reach the final, so Nadal blinked first. Most of Nadal mistakes were forced by the fact that Federer was playing on the base line, if not inside the court (as you could see from how many half-volleys he fired from that position). This takes a lot of time away from anyone. The second set was decided on a detail: what would have happened if that ball on 30 all haven´t clipped the net? Would it be deep enough to trouble Nadal (as Federer was already going to the net)? Federer´s return on the break point was deep and close the right side line, a few inches more and it would be out.
There were two very long, very good rallies on the final game -- both players hitting hard with the match on the line. The match statistics are good. So the hard facts point clearly to a good match, to a good showing by both.
Honestly, for the first time this year, I saw Nadal go toe to toe with Federer, and let things competitive (as himself said on his post match). In AO, honestly, he was basically gifted two sets by poor play from Federer. In IW it was what it was. This time, it was decided on details.