nicklaus was hugely impressed by spieth 's four-shot win over justin rose and phil mickelson .
the 21-year-old spieth equalled tiger woods ' 72-hole record and became the first man to get to 19-under par at augusta .
the 21-year-old , who was second last year , moved from fourth in the world rankings to second behind rory mcilroy as a result and that means the world 's top two players have a combined age of 46 .