After a startling upset in Sri Lanka’s presidential election, President Mahinda Rajapaksa conceded defeat on Friday morning, bringing an abrupt end to a larger-than-life, increasingly controlling presidency that he had hoped to extend into a third six-year term. Mr. Rajapaksa left his residence, Temple Trees, shortly after 6 a.m. “to allow the new president to assume his duties,” a presidential spokesman announced. Mr. Rajapaksa’s defeat is remarkable because he had an overwhelming advantage going into the election, which he decided to hold two years ahead of schedule. During nearly a decade in office, he had built close ties with China,...