Subroutes middlewares with Gorilla MUX and Negroni

I'm trying to add a middleware only on some routes. I wrote this code:

func main() {
  router := mux.NewRouter().StrictSlash(false)

  admin_subrouter := router.PathPrefix("/admin").Subrouter()

  //handlers.CombinedLoggingHandler comes from gorilla/handlers
  router.PathPrefix("/admin").Handler(negroni.New(
	negroni.Wrap(handlers.CombinedLoggingHandler(os.Stdout, admin_subrouter)),
  ))

  admin_subrouter.HandleFunc("/articles/new", articles_new).Methods("GET")
  admin_subrouter.HandleFunc("/articles", articles_index).Methods("GET")
  admin_subrouter.HandleFunc("/articles", articles_create).Methods("POST")

  n := negroni.New()
  n.UseHandler(router)
  http.ListenAndServe(":3000", n)

}

I expect to see request logs only for paths with prefix /admin. I do see a log line when I do "GET /admin", but not when I do "GET /admin/articles/new". I tried by brute force other combinations but I can't get it. What's wrong with my code?

I saw other ways, like wrapping the HandlerFunc on each route definition, but I wanted to do it once for a prefix or a subrouter.

The logging middleware I'm using there is for testing, maybe an Auth middleware makes more sense, but I just wanted to make it work.

Thanks!

Issue is the way you create an sub routes /admin. Complete reference code is here https://play.golang.org/p/zb_79oHJed

// Admin
adminBase := mux.NewRouter()
router.PathPrefix("/admin").Handler(negroni.New(
	// This logger only applicable to /admin routes
	negroni.HandlerFunc(justTestLogger),
	// add your handlers here which is only appilcable to `/admin` routes
	negroni.Wrap(adminBase),
))

adminRoutes := adminBase.PathPrefix("/admin").Subrouter()
adminRoutes.HandleFunc("/articles/new", articleNewHandler).Methods("GET")

Now, access these URLs. You will see logs only for /admin sub routes.