Indian Prime Minister Narendra Modi and Russian President Vladimir Putin got straight down to talks on Thursday on boosting nuclear and defence cooperation at a summit aimed at reviving an old friendship that has faded over the years.
Putin's one-day visit to India comes at a time when Russia is at odds with the West over Ukraine, and its economy is stalling as oil prices tumble to their lowest in five years.
The tension over Ukraine intruded on the choreographed visit when it emerged that the leader of Crimea, the former Ukrainian territory annexed by Russia, had travelled with Putin to India for unofficial talks to enhance trade.
India does not support Western sanctions against Russia, but the Crimean leader's presence may prove an irritant before US President Barack Obama visits India next month.
Modi, elected by a landslide six months ago, is expected to give Obama a far more lavish reception as chief guest of India's Republic Day celebrations than Thursday's formal summitry.
Yet Moscow's eye has wandered too since its Soviet-era romance with New Delhi. Bilateral trade, at $10 billion, is now one-ninth of that between Russia and China - the focus of Putin's pivot away from an increasingly critical Europe.
"Russia is a tried and trusted friend - a country that has helped us in times of trouble," an Indian official told Reuters. "But that friendship hasn't delivered in terms of its economic potential."
The two leaders presided over the signing of a "vision" document setting out a roadmap for cooperation over an extended period, with the most ambitious area nuclear energy.
Russia's state-owned Rosatom said that under an agreement signed on Thursday it would supply 12 nuclear energy reactors for India over 20 years.
A 1,000-megawatt reactor is operating at the Russian-built Kudankulam power station in south India, with a second due onstream in 2015. Putin had been pushing for Rosatom to increase the number of reactors it could supply to as many as 25.
Indian officials say a total of six reactors will be built at Kudankulam, with a further six to follow at a site that has not yet been determined.
Other strategic deals were expected to cover oil exploration and supply, infrastructure and an increase in direct diamond sales to India by Russian state monopoly Alrosa.
On defence, the two sides will seek to move ahead with long-delayed projects to develop a joint fifth-generation fighter jet and a multi-role transport aircraft.
A spokesman for India's foreign minister said he was not officially aware of Crimean leader Sergey Aksyonov's visit.
Gul Kripalani, a Mumbai businessman who met the Crimean leader at a New Delhi hotel as head of the Indian-Crimean Partnership, told Reuters the talks were unofficial and Aksyonov had "happened to be on the flight with His Excellency President Putin".
Western countries imposed sanctions against Russia over the annexation of Crimea in February and the Kremlin's support for an uprising by pro-Russian rebels in eastern Ukraine.