Grealish came off the substitutes' bench at half-time against local rivals Birmingham City, and helped to turn the match in Villa's favour.
The 19-year-old was a constant menace when on the pitch, and his display earned plenty of praise from Yorke, who is clearly very excited about his potential.
"The kid is very aware, and that's why a lot has been said about him," he said. "He takes up clever positions, and he uses the ball really well - his selection of passes is great.
"Every time I have seen him he has impressed me every time. He has talent in abundance. He's just a very clever footballer, and his introduction made a massive difference. He's a touch of class, and he could be the real deal."
Villa beat Birmingham thanks to a header from Rudy Gestede, but it was Grealish's introduction, alongside Jordan Ayew, which made the biggest difference in the contest.
The Claret and Blues had been miles off the pace in the first 45 minutes, but they were a changed team after the interval and ultimately deserved their victory.
It was just another showing of Grealish's obvious quality, which has made him such a key part of Villa's team since being handed an opportunity by Tim Sherwood.
The attacking midfielder carries much of Villa's creative burden, and there are high hopes for his future with the Midlands side.