Hartley added that he expects the three remaining clashes with Rangers to decide the destination of the title.
"Everyone's already talking about the three Old Firm games deciding the title. There are a lot of big games between now and then but this is what it all comes down to."
Looking ahead to Wednesday's Champions League showdown with Barcelona, the midfielder says there's no reason to be afraid of the Spanish giants.
"Our home form is as good as anyone's in the Champions League so we fear no one these days. We can beat anyone on our day so we won't be afraid of Barcelona going into this one. They are a quality side but if we put in the same sort of performance as we did against Milan and Donetsk in the group stages then we've got a chance."
"These games are why you come to a side like Celtic."