The Union of Concerned Scientists did the best and most rigorous assessment of the carbon footprint of Tesla's and other electric vehicles vs internal combustion vehicles including hybrids. They found that the manufacturing of a full-sized Tesla Model S rear-wheel drive car with an 85 KWH battery was equivalent to a full-sized internal combustion car except for the battery, which added 15% or one metric ton of CO2 emissions to the total manufacturing.
However, they found that this was trivial compared to the emissions avoided due to not burning fossil fuels to move the car. Before anyone says "But electricity is generated from coal!", they took that into account too, and it's included in the 53% overall reduction.