NEW DELHI: 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 organising the opposition against pro-China Rajapaksa.

His successor, President Maithripala Sirisena, has said 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 development in Colombo that would give Beijing a strategic toehold on India's doorstep.

India has pushed back against China elsewhere in the region since Prime Minister Narendra Modi took office in May, improving ties with Japan and Vietnam, both locked in territorial disputes with Beijing, and contesting a port project in Bangladesh that could otherwise have been a cakewalk for China.

The new robust diplomacy, which Modi calls “Act East”, has delighted Washington, which has been nudging India for years to dovetail with the US strategic pivot toward the region.