In 2009 he defeated the CPI's P Ramachandran Nair by nearly one lakh votes and polled over 14 percent more.
In 2014 he edged the BJP's O Rajagopal by fewer than 16,000 votes.
Five years later the margin was much healthier and Tharoor thumped the BJP's K Rajasekharan by one lakh votes.
Exit polls had suggested Chandrasekhar would defeat his rival.