Mark's only previous experience in the first team was against Southend United in the first round of the Carling Cup, but he looked far from out of his depth when he came on for Adam Nowland at Stamford Bridge after Chelsea had scored.
"It was just overwhelming, really; the gaffer said to me 'get ready' and there were still 35 minutes to go - I was over the moon to get out there against some of the best players in the world.
"The gaffer showed a little bit of trust in me and it is unbelievable."
Adds Alan Pardew:
"Mark actually thanked me for the opportunity of playing but he didn't need to because it was his ability that got him there."
Continues Mark:
"I was just told to get involved in the game and to do what I can do, to try my best all the time; I didn't lose the ball or anything so I was quite pleased.
"I found it all right because obviously there are good players around me and they know what has to be done.
"And in the Premier League they stand off you a bit so you have got more time on the ball."
Mark insists that facing Chelsea's multi-million pound stars did not faze him and he adds:
"You just play what is put in front of you and in a big crowd you can't really hear a lot - so you don't really think about doing anything other than your own game.
"You forget about the big players because that doesn't mean anything to you when you are out there, does it?
"It is obviously good to play against those players and if I have kids I can tell them I have played against the likes of Frank Lampard, Tiago, Duff, and the rest, which is great."
Shortly after coming on, mark made a shuddering challenge on Scott Parker that was slightly mistimed, and he jokes:
"That is payback for the reserve game when we lost 5-1!
"I thought I win the ball, but I didn't."
Mark was thought by many of the Chelsea players to be the standout Hammer in last month's reserve encounter between the two clubs, and Mark is keeping his feet on the ground, knowing that his next action might be reserve team football once more.
"It was training today and back to basics," he smiles, "but it was just a great feeling for all my family and everyone I know, for me to play for West Ham, the team I love and where I was brought up.
"I think the fans should be proud because Chelsea have so much money it is unbelievable and they can buy whoever they want in the world.
"The boys tried really hard, we passed the ball a lot and dominated the game at times.
"It is a beautiful stadium, it is just the sort of place you want to play - as well as Upton Park - and we want to be facing the best teams at the best grounds every week next season."
Of the overall performance, Mark says:
"Some teams get beaten 5-0 or whatever against teams like that in these cups, and we have put a strong performance in with a lot of players missing.
"It might even have been different with those players but, that said, the ones that did play have done credit to themselves."
Mark even thought that Anton Ferdinand had earned West Ham a reprieve with his late header that hit the woodwork, and he says:
"I thought it was in, myself; it was a great header and I don't know how he got up there so quickly."