Moda Center, understandably, found itself in a stunned silence after the San Antonio Spurs turned a 15-point second-half deficit into a 120-108 win over the Trail Blazers in Game 3. But, make no mistake about it: with a chance to tie the series on Sunday afternoon, Portland will be packed with energy. Obstacles will run aplenty, as Portland attempts to tie the series at two games apiece; here are three storylines worth keeping tabs on: The Mental Aspect of Game 3’s Collapse: There’s no way to sugarcoat it, since Portland has already admitted that Game 3’s loss was the type of defeat one would “lose sleep over.”   The cliches are ones we’ve heard time-and-time again throughout professional sports: “next game mentality,” “flushing” a regrettable performance — pick your favorite phrase. The reality remains the same: when the Blazers touch Moda Center in Game 4, they’ll arrive as a team that let a 15-point third quarter edge — and a 2-1 series advantage — slip through its fingertips.…