The match statistics don't indicate any great difference in performance between David and Daniel with the exception of break points.
|1st serve %||57%||60%|
|1st serve points won||60%||63%|
|2nd serve points won||53%||47%|
|break points won||5/13||5/9|
Koellerer clearly faced stiff competition from David but was able to hold his own while David was simply unable to convert enough break points to make a difference. This was particularly telling near the end of the match when David was a break down and led 40-0 on Koellerer's serve but was unable to convert any of these three critical break points. That must have been demoralizing and a sure sign that he simply couldn't manage to break back.
This is Daniel Koellerer's first match win on the ATP tour. It is incomprehensible that it was a player of David's calibre who gave him his first opportunity.