Not entirely right. Remi Coulom's Monte Carlo Tree Search, in 2006, was the first really big discovery. It didn't make engines good enough to beat the best humans, but it steadily made them good enough to beat 99% of go playing humans, playing at up to 6 - 7 dan level. It was still part of AlphaGo, too (though as I recall AlphaGo Zero did away with it).