How can I translate my prefab on Instantiate?

I'm trying to spawn a prefab on a GUI Button click and put it in a specific position.

I can create the object but any attempts to position it after creation inside the onclick function do not work, it always stays at (0,0,0). Can someone please unlock the mystery as to why I can't re-position the prefab on creation? I've tried setting it manually, setting it via the Instantiate command, etc. Here's my code below.

 using UnityEngine;
 using System.Collections;
 
 public class StartGame : MonoBehaviour {
 
     GameObject [] tiles = new GameObject[1];
     
     float speed = 1;
     
     void OnGUI () {
         // Make a background box
         GUI.Box(new Rect(10,10,100,90), "Menu");
 
             if(GUI.Button(new Rect(20,40,80,20), "Spawn")) {
                  tiles[0] = Instantiate(Resources.Load("tilePrefab")) as GameObject;
                  //tiles[0] = Instantiate(Resources.Load("tilePrefab"), 
                  //   new Vector3(-2,0,0),
                  //   Quaternion.identity);
                  tiles[0].transform.position = new Vector3(-2,0,0);
             }

 }