Including "Chapter" before each section number in the ToC? (Article Class)

Here is a solution. I didn't load tocloft, since I use titletoc. Also I added a formatting for thoe unnumbered sections which should appear in the table of contents:

 documentclass[12pt]{article}
usepackage[utf8]{inputenc}
usepackage[english]{babel}
usepackage[showframe]{geometry}
usepackage{titlesec}
usepackage{titletoc}

addtocaptionsenglish{ renewcommand*contentsname{centerline{TABLE OF CONTENTS}}}

titleformat{section}[display]%
{nullvskip1emsffamilybfseriesfilcenter}{Chapter thesection}{0em}{}[]
titleformat{name = section, numberless}[block]%
{nullvskip1emsffamilybfseriesfilcenter}{}{0em}{}
titlespacing*{section}{0em}{1em}{1em}

titlecontents{section}
[7em] % ie, width of contentslabel + 0.5em
{medskip}
{contentslabel[MakeUppercasechaptername~thecontentslabel]{6.5em}}%thecontentslabel
{hspace*{-6.5em}}
{titlerule*[0.5pc]{.}contentspage}

begin{document}

tableofcontents
newpage

section*{An Unnumbered Section}
addcontentsline{toc}{section}{An Unnumbered Section}
section{Section One}
subsection{A first subsection}
section{Section Two}
Content

end{document} 

I am editing a book using tstextbook, which includes use of package titletoc.

Solutions given in this thread did not helped me. Because of package titlesec introduce too many error in my compilation, resulting in a bigger problems that that I was trying to solve. The same case when I tried to test solutions that use package tocloft.

After some hours researching and testing, my solution is simple: just by modifying the of the titlecontents command for "chapter".

My original entry:

{color{tssteelblue}contentslabel[Largethecontentslabel]{1.25cm}} %ORIGINAL

A working solution:

{chaptername thecontentslabel:quad}% <numbered-entry-format> %It compiled within my code without errors!!!

My final solution, that solved my requirement:

{color{tssteelblue}Largechaptername thecontentslabel.space} %Final solution

*Please consider that my book is in Spanish.

My final complete code for chapter:

%titlecontents{ <section> }[ <left> ]
%{ <above-code> }
%{ <numbered-entry-format> }{ <numberless-entry-format> }
%{ <filler-page-format> }[ <below-code> ]

titlecontents{chapter}[0cm]
{addvspace{14pt}largesffamilybfseries}
{color{tssteelblue}Largechaptername thecontentslabel.space} %Final solution
{}
{color{tssteelblue}normalsizesffamilybfseries;titlerule*[.5pc]{.};thecontentspage}

My solution given from here