Hartley said: “Martin has been terrific. He’s been champing at the bit for the last couple of weeks for a start.
“He’s been doing well in the reserves and I thought he did well when he came on against Hamilton. So he deserved his start on Saturday. He showed what a threat he is.
“I spoke to him and said if you start adding some consistency to your game it can make the difference. He’s got the pace so it’s just about the final product, which is the pass or whatever.
“It’s all about being a bit more calm and composed in the final third. I was really pleased for him at the weekend and now he needs to find consistency to become a first-team pick.”
The Dundee boss also reflected on the win at Kilmarnock.
The manager said: “The spirits are high. Everyone feels better when you come into the club in the morning on the back of three straight wins.
“It was a good performance down at Kilmarnock. We had a little blip recently which we always knew would come but we’ve reacted well.
“Now we can go into Saturday’s game with St Johnstone full of confidence. The players will be bouncing and rightly so.”