Conor McGregor, Holly Holm -- Even the Losers Celebrate

Conor McGregor and Holly Holm were light on their feet at their UFC after parties in Vegas ... lighter because they weren't weighted down by their championship belts.

Conor was at Surrender Nightclub at the Encore hotel and stayed past 3:30 AM ... and it seemed he was feeling no pain, although he must have been after getting pounded into the ground by Nate Diaz.

As for Holly, she arrived at same party at around 2 AM and beelined it for the VIP section.