Yes, even in the sparkling new Barclays Center, there was plenty of dust flittering about Tuesday night. There will be plenty more on Thursday. Throat lumps and goose bumps and all manner of sentiment were coursing through the veins of the CeltNets, Paul Pierce and Kevin Garnett. With more to come. Tuesday, it was the Celtics. Thursday it will be Doc Rivers. Reunion Week at Barclays. Part one was a splendid chapter, the Nets playing their best end-to-end game of the year, beating the C’s 104-96, giving the CeltNets the win in their first meeting against the team for whom they lifted a 17th banner. Thursday it’s Rivers who, if he’d had his way, would’ve conducted this reunion 3,000 miles away, in Los Angeles, the three of them making like an old vaudeville act, trying to make one last championship go of things alongside Chris Paul and Blake Griffin. Touching stuff, all of it. For the Nets, though, it wasn’t nearly their most interesting or important reunion of the week: the one between Deron Williams and his teammates, between Williams and Nets fans, between Williams and the course these Nets want to set before things blew too far adrift. That’s the big one. And, after the band has been back together for 48 minutes, a feel-good one, too. “Watching these games, I knew we’d been a little stagnant at times,” Williams said after contributing 25 points (thanks to highly efficient 10-for-16 from the floor) and seven assists to this victory, his first after missing nine straight games with a bum ankle. “We needed to pick up the tempo and the pace. And I wanted to get us going early.” It was precisely the kind of performance Williams has hinted at throughout his time with the Nets, Jersey side and Brooklyn side, the kind he has teased us with for small swatches and longer stretches but rarely for any meaningful kind of run. Last February, when the Nets made a final push at the Knicks atop the Atlantic, he played like this.