Olympics 2012 for me. He simply outplayed Fed,but ,like in many matches, Fed was saved by serve.
Olympics 2016 was painfull as well,but it was obvious he's gonna lose. He was exhausted.
Del Potro gradually improved against Federer at the Slams throughout 2009. After getting his backside handed to him at the AO, he took Fed to 5 sets at RG and narrowly lost. Then he took him to 5 sets at the US Open and narrowly won. Wawrinka's famous tattoo "Ever tried. Ever failed. No matter. Try again.Fail again. Fail better" surely couldn't have applied better than to Del Potro's efforts against Federer at the 2009 Slams!
Slight correction though, @TheMaestro1990. AO 2009 wasn't Delpo's first slam QF. It was his second. His first GS QF was USO 2008, where he lost in a tight match to Sir Andy Murray
I will rule out the FO and Wimby semis.
He did more than expected on both occassions and he was simply outplayed. Had no right to win any of the 2 matches in the end.
2016 Olympics:did wayyy more than expected already. He came into the final gassed and was routined by Murray in a match with virtually no drama.
The losses in Masters+ 2009 Tour Finals ain't that bad overall.
Slight correction though, @TheMaestro1990. AO 2009 wasn't Delpo's first slam QF. It was his second. His first GS QF was USO 2008, where he lost in a tight match to Sir Andy Murray