The Senegalese midfielder signed with the Potters from Galatasaray last month in a deal worth £14m.
"I thought he was excellent," Lambert enthused. "What a debut that was, I thought he was brilliant.
"It was his first training session for about 10 days (on Friday) and even then it was a kind of walk through because of playing on the Wednesday. But I thought his level was excellent.
"I knew fatigue would set in with the lad in his first game and he's got a yellow card, so with fatigue he could mis-time a challenge and then you're down to 10 men and lose him for the following game.
"It was the right thing to do for him (subbing him in the 71st minute) because of the way was going.
"He will have a good week this week coming and what you see there, there will be a lot more of that to come.
"The club asked me would I have a look at him and I watched videos of him playing games and I could see within two minutes the boy could play.
"I liked everything about him. Up and down, up and down, energetic, which we needed, and it was a matter of me saying `Yes' or `No.'
"I liked the way he was driving with the ball, we needed somebody to do that, and if he can add that every single week we have a hell of a player on our hands."