In PRO sports I don't do that... for the most part. IF there is a certain player I like from the team MY team is playing I will have some sympathy for him/her... but that's the breaks.
With youth, and by that I mean pre-Pro, I often can feel great sympathy for the loser.
Just had a similar experience as yours... was watching my niece play tennis - her opponents Dad was there. My nieces opponent was a tiny little asian girl (doubt she weighed 80lbs) but she could generate incredible power. Her Dad stood right next to us. Spoke to us during the entire match. Afterwards her tears WERE of the 'boo-hoo' type BUT... with a big smile and lots of congratulations to my niece. Watching it happen I was stoic... on the outside. Inside it was ripping my heart out.