Djokovic squandered a golden opportunity to tie Federer's 6 YEC and tie Sampras 6 YE #1.
Entering WTF, Djokovic had an excellent tie-break record this year, yet, he blew a 4-1 lead in a third set tie-breaker against Thiem and loses the match. Despite of a disappointing loss, he still had a great chance to qualify for the semifinal since his next match was against a 38 years old Federer who was a huge underdog.
All he needed was to win one match to qualify for the semifinal but instead he lost both matches. Opportunity only knocks once and he only had himself to blame.
Yeah, that match against Thiem really stings because Novak should have won it. Either at 30-30 in the 10th game of the 3rd set (when Novak looked to be playing better than Thiem, had the momentum on his side and really ought to have broken him), or from when he was 4--1 up in the tie break. To let Thiem rattle off 5 consecutive points from that stage-- puzzling. Not something one would expect a clutch, steely player like Novak to do.
There was no way he was beating Fed in that RR match, though. 38 years or whatever, Fed played awesome and Novak really did not have a chance against him on that day, that match. Had Novak won against Thiem though, Fed and Novak would have qualified as 1 & 2 from Group Bjorn Borg, and Novak would be facing Tsitsipas in the semi today. Very, very doable; considering the fact that Tsitsipas has never been at this stage before and would surely be exhausted after his RR match with Rafa.
But, just to play devil's advocate -- Had Novak beaten Thiem, it's worthwhile to wonder whether Thiem would have pushed harder and eked out a win in 3 sets at least, against Berretini. I'm not saying Thiem tanked that last match, sure he didn't. But surely, he would have pushed a lot harder had his qualification been on the line. If that happened, and we had 2 counterfactual results- Novak defeating Thiem and then Thiem defeating Berretini - we would still have Novak (unfortunately) eliminated from the semis.
So in sum, it is what it is. Hope Novak takes some time off to recoup and re-energise - not just physically but also from his extremely
flat , passive approach which plagued the end of his match with Thiem and the entirety of his match with Fed.