The first giant hit from Yes was the Yes Album in Feb. 1971. It hit no. 4 on the UK charts, #40 on the Billboard 200 and certified platinum.
The Yes Album was so unique and different from what was being done that it would stop people in their tracks. It's rare when a new sound comes along and even rarer still when its allowed to flourish by an industry that is traditionally known for me-too sound-a-like whoredom.