Castillo, who was born and raised in the USA, joined Santos Laguna in 2005 and has been a starter since January of 2007. He has dual citizenship and has represented Mexico at the U-23 and full national team level. He won his starting spot while Santos was fighting relegation.
Santos finished second in the overall standings of the Clausura 2008 season. Castillo started each of Santos' six playoff games, which included a 2-1 first leg final win at Cruz Azul.
The title marked the third in Santos' history, having won in 1996 and 2001.
In the second leg, Jaime Lozano equalized in the 83rd minute but Santos held on for the tie that gave it the win on aggregate.