The young attacking midfielder has had to be patient in waiting for his chance since breaking through in the final game of last season against Wolves. He enjoyed a loan stint at Swindon this season having, last season, spent three months at Brighton.
The Republic of Ireland under-21 international nearly saw some action at Old Trafford on Tuesday and was taken to the line by the fourth official, but events took over and Martin Jol opted for the defensive security of Anthony Gardner instead.
"I was just delighted to get on," beamed a naturally happy 'Yeatesy' afterwards. "It is a bit frustrating now because I thought I could have got my first goal out there. Hopefully it is the first of many games now.
"I had a little feeling I would get on, but it has been so long since I've had a proper football game and you forget the pace of it. When I got out there it was flying everywhere, but I think I did okay and looked lively."
Despite his spell at the Withdean Stadium, Mark still received a little good natured flak from the visiting Brighton thousands.
"When I was warming up they gave me a little clap and I think it was just a bit of banter more than anything. They are a good bunch, a fair few travelled and made a lot of noise."
As he mentioned above, Mark did have a couple of chances to score after coming on but delayed his shots and opted against passing. He admits people might suspect he is a little greedy, but insists it was simply a desire to make a positive impression on the fans.
"They probably do! I should have passed and looked around me but I was so anxious to get out there and that is why. I was a bit unlucky."
Mark Yeates was thrilled to get his opening first team action of the season when he came off the bench for a late cameo appearance against Brighton.