Right out of the gate
I know Steve Ditko served an apprenticeship in comics; he worked in the Simon & Kirby stable for awhile, where he was reportedly influenced by Mort Meskin (who also influenced Joe Kubert). But it's not stretching things (hyuk hyuk) to say when Ditko went solo he came right out of the gate as a solid professional. He showed even in his earliest stories that he stretched head and shoulders above many of his contemporaries in the industry.
...and speaking of stretching...
..."Stretching Things" was Ditko's first solo story, although not his first published story. It appeared in Fantastic Fears #5, and this is a black and white reprint from 1971, Terror Tales Vol. 3 No. 4.
I'm also including an early crime story to show that even in otherwise routine stories his artwork elevated the material. It's from Charlton's Crime and Justice #18, 1954.
You can read the original color version of "Stretching Things" at The Horrors Of It All.