I was thinking earlier this year (mostly around AO '13) about the most heartbreaking GS losses.
I know there are many more than this but these are the few that come to my mind:
Li Na - AO '12 & AO '13
Clijsters - FO '01
Dementieva - W '09
Jankovic - '06
(I wanted to include a poll, but I'm too noob to know what to do)
Also, I understand many will use the argument of 'none because they all deserved to lose because they never seized their chance when they had it etcetc.' which is fair enough I suppose.
A few off the top of my head. Obviously the most notable one was Novotna after the final of Wimbledon 1993. The most distraught depiction of a tennis player up to that point.
I think Venus's Wimbledon final loss to Serena in '09 demoralised her beyond repair after that, especially in big matches.
That would have been my pick. I was very happy for Sveta, but Dinara during that match was really quite sad. I've never seen anyone so consumed by their helplessness.
I dont look at Dementieva's loss to Serena as heartbreaking because Venus was in the final, and its hard to beat both Serena & Venus at Wimbledon.
Davenport having a championship point, then back problems in 2005, that one must still hurt. Her last slam win was Jan. 2000.
Hantuchova against Ivanovic at 2008 AO, because that would have been a career best at a major for Dani, a slam final.
Also Cornet having match points against Safina at 2009 AO, that might have hurt her career
I agree Serena at French Open QF loses and 1st round, she was there but got tight.
Also Dani's AO loss, wonder what would have happened to her career if she didn't choke.
I remember the following year ESPN showed the match during a rain delay. I watched all of one point before turning it off. It still hurt too much then, and still hurts too much now.
RG/W/UO F 2002; AO F 2003: Losing to Serena 4 times in a Row in a slam final
UO 2005 SF: Losing to Clijsters after being up 6-4 4-2
UO 2008 QF: Losing to Serena 6-7 6-7 despite having setpoints in each set
W 2009 F: Losing to Serena in the final of Venus' favorite slam hurt her confidence forever and she hasn't been the same mentally since
AO 2010 QF: Losing to Li Na despite being up 6-2 5-3
UO 2010 SF: Losing to Clijsters after being up 6-4 6-6 and playing the worst tiebreak I have ever seen