You can catch a bus (guagua) directly to Mao from the bus station at what they call the rotunda de Mao at the end of avenue Sadhalla. It isn't a rotunda anymore but traffic lights! There are bus stations on both sides of the road and you want the one on the Santiago side. Just ask anyone for the guagua. Cost is around 200 pesos I think and will take 45 mins to an hour.