Based on the previous 47 minutes, they should have known what was going to happen. Wesley Matthews, successful at wriggling free for shots all night, caught the ball on the right side of the circle, dribbled right, and with 53.6 seconds left buried a 3-pointer that sank the Celtics for the third time in their past four games. Their 92-86 loss to the Blazers dropped the C’s to 1-3 on this western road trip, with the finale tonight in Salt Lake City in front of one of the toughest home crowds in the NBA. And they will be coming off a winnable game that always seemed to be one possession out of reach. Matthews, who had the microwave on high all night, was one reason with a 24-point, five-trey performance. But it wasn’t that last shot that bothered Doc Rivers. “Wes made it tough. That last 3 was a step-back 3 going to his right,” the Celtics coach said. “God bless him. He’s done it all year.” Rivers, instead, had a problem with the first four 3-pointers, just as he was bothered by everything else, from poor ball movement to worse rebounding. “Some of it was good offense, but some of it we didn’t play defense the way we are capable of,” he said. “I can live with that. But it’s the other ones, where we’re standing there and you lose sight of him. Wes is a smart player and he can make shots. “It was one of those ‘my bad’ games,” Rivers said. “I told the guys we had so many ‘my faults,’ where we lost sight of guys, offensive rebounds. We didn’t finish any quarter right. Every quarter they made a run. Halftime, end of the fourth quarter, end of the third. It was a gettable game. But give them credit. They hit some big shots.”