When Sri Lanka unexpectedly turfed out President Mahinda Rajapaksa in an election this month, it was the biggest setback in decades for China's expansion into South Asia — and a remarkable diplomatic victory for India.

Despite New Delhi's protestations, diplomats and politicians in the region say India played a role in organizing the opposition against the pro-China Rajapaksa.

His successor, President Maithripala Sirisena, has said that India is the "first, main concern" of his foreign policy and that he will review all projects awarded to Chinese firms, including a sea reclamation project in Colombo that would give Beijing a strategic toehold on India's doorstep.