The easiest way is to extract the JSON and then unmarshal it into a struct. The \uXXXX parts are unicode characters

package main

import (
    "encoding/json"
    "fmt"
    "regexp"
)

// Data follows the structure of the JSON data in the response
type Data struct {
    HTMLInfo  string `json:"htmlInfo"`
    OtherInfo string `json:"otherInfo"`
    MoreInfo  string `json:"moreInfo"`
}

func main() {
    // input is an example of the raw response data. It's probably a []byte if
    // you got it from ioutil.ReadAll(resp.Body)
    input := []byte(`this=ajax({"htmlInfo":"\u003Cdiv class=\u0022container columns-2\u0022\u003E\n\n \u003Csection class=\u0022col-main\u0022\u003E\n \r\n\u003Cdiv class=\u0027visor-article-list list list-view-recent\u0027 \u003E\r\n\u003Cdiv class=\u0027grid_item visor-article-teaser list_default\u0027 \u003E\n \u003Ca class=\u0027grid_img\u0027 href=\u0027/manUnited-is-the-best\u0027\u003E\n \u003Cimg src=\u0022http://example.com/sites//files/styles/w400h22", "otherInfo": "Blah Blah", "moreInfo": "Bleh Bleh"})`)

    // First we want to extract the data json using regex with a capture group.
    dataRegex, err := regexp.Compile("ajax\\((.*)\\)")
    if err != nil {
        fmt.Println("regex failed to compile:", err)
        return
    }

    // FindSubmatch should return two matches:
    // 0: The full match
    // 1: The contents of the capture group (what we want)
    matches := dataRegex.FindSubmatch(input)
    if len(matches) != 2 {
        fmt.Println("incorrect number of match results:", len(matches))
        return
    }
    dataJSON := matches[1]

    // Since the data is in JSON format, we can unmarshal it into a struct.  If
    // you don't care at all about the fields other than "htmlInfo", you can
    // omit them from the struct.
    data := &Data{}
    if err := json.Unmarshal(dataJSON, data); err != nil {
        fmt.Println("failed to unmarshal data json:", err)
    }

    // You now have access to the "htmlInfo" property
    fmt.Println("HTML INFO:", data.HTMLInfo)
}

Which will produce:

HTML INFO: <div class="container columns-2">

 <section class="col-main">

<div class='visor-article-list list list-view-recent' >
<div class='grid_item visor-article-teaser list_default' >
 <a class='grid_img' href='/manUnited-is-the-best'>
 <img src="http://example.com/sites//files/styles/w400h22