"Half as likely as" or "Half as likely than"?

Which of the two following sentences is correct?

"Group A is less than half as likely to succeed as Group B."
"Group A is less than half as likely to succeed than Group B."

I know that normally, a sentence would be "Group A is less likely to succeed than Group B," but I am wondering whether the "than half as" changes the structure.

Thanks.

We use 'than' in statements of simple comparison. Bill is older than Rachel. Canada is bigger than Japan. I am shorter than my brother. Steel is stronger than wood.

Comparison: clauses

We use 'as' when comparing equality (or the lack of it). Mary is as tall as Peter. My car cost half as much as yours. Your house is nearly twice as big as mine. Group A is less than half as likely to succeed as Group B.

Comparisons of equality