The Spurs might suck this season, but one fan single-handedly made Sunday's game a whole lot better ... by absolutely dominating a lip sync challenge to Kelly Clarkson's "Since U Been Gone."
It all went down at the AT&T Center in San Antonio during the Spurs' matchup against the Portland Trail Blazers ... when the jumbotron cam focused in on 27-year-old Briana Saldaña to show off her skills -- and she didn't hold back.
Check out the awesome vid -- Briana jumps from her seat and uses her drink as a makeshift microphone .