As thousands of troops prepared on Monday for a dazzling military parade for Republic Day where US President Barack Obama will be the chief guest, rain threatened to dampen the excitement around his landmark visit to the country.
Obama, who is the first US president to attend the annual show of military might that was long associated with the anti-Americanism of the Cold War, spent the first day of his visit on Sunday bonding with Prime Minister Narendra Modi and sealing a clutch of deals.
The two leaders announced plans to unlock billions of dollars in nuclear trade and to deepen defence ties, steps they hope will establish an enduring strategic partnership.
Most significant was an agreement on two issues that, despite a groundbreaking 2006 pact, had stopped US-based companies from setting up nuclear reactors in the country and had become one of the major irritants in bilateral relations.
The bonhomie was a remarkable spectacle, given that a year ago the Prime Minister was banned from visiting the US for nearly a decade after deadly Hindu-Muslim riots in Gujarat when Modi was the cheif minister.
Obama is the chief guest for Republic Day celebrations in the national capital, where tanks, troops and floats showcasing the country's cultural diversity will pass along Rajpath that connects the Rashtrapati Bhawan to India Gate.
Despite on-off rain and overcast skies, tens of thousands were gathered along the route for the annual parade.
Security was tight at the parade and across the city, where tens of thousands of police and paramilitary personnel were deployed on street corners and rooftops.
Obama's presence at the parade - at Modi's personal invitation - marks the latest upturn in a roller-coaster bilateral relationship that just a year ago was in tatters.
Bickering over protectionism culminated in a fiery diplomatic spat in 2013 and the abrupt departure of the US ambassador from New Delhi, who has only just been replaced.
The United States views India as a vast market and potential counterweight in Asia to a more assertive China, but has frequently been frustrated with the slow pace of New Delhi's economic reforms and unwillingness to side with Washington in international affairs.
Elected Prime Minister in May 2104, Modi has injected a new vitality into the economy and foreign relations and, to Washington's delight, has begun pushing back against China across Asia.
The two leaders emerged from their talks on Sunday with a 10-year framework for defence ties and deals on cooperation that included the joint production of drone aircraft and equipment for Lockheed Martin Corp's C-130 military transport plane.
Other deals ranged from an Obama-Modi hotline - the country's first at a leadership level - to financing initiatives aimed at helping the country use renewable energy to lower carbon intensity.
The US President also enjoyed a close friendship with Modi's predecessor Manmohan Singh, who staked his premiership on the controversial nuclear deal that made India the sixth "legitimate" atomic power and marked a high point in Indo-US relations.
The deal failed to deliver on a promise of business for US firms because of the country's reluctance to shield suppliers from liability, a deviation from international norms that reflects the memory of the Bhopal industrial disaster.
Obama will leave the country slightly earlier than first scheduled to travel to Saudi Arabia following the death of King Abdullah, skipping a planned visit to the Taj Mahal.