OKLAHOMA CITY — It took 50 days, 20 games and 10 different opponents. It took the highest scorer in the NBA, the loudest crowd and the best sixth man. It took a poised point guard, a proven defensive stopper and an inspired front line. But the Oklahoma City Thunder did what no one has been able to do since Tax Day. They beat the San Antonio Spurs. The Thunder didn’t just snap the streak, they sawed it in pieces, treating San Antonio the way the Spurs have been treating everybody else for the past two months.