James McPake gave Dundee the lead in the first minute of the game with a great header from Phil Robert’s corner.
However, unfortunately former Dundee player Leigh Griffiths scored the equaliser on 55 minutes.
It was another good performance by the home team and Hartley revealed how he and his team prepared for the match.
“We have watched a lot of footage of Celtic over the last couple of weeks,” Hartley said. “We even showed the players more of that footage before they went out today.
“We have watched Celtic’s last (set) of games for hours, looking at how we could hurt them. So we worked all week on how we wanted to play today.
“I told them to try to get in behind Celtic, turn them and try to play the match in their half.”