Since his return from a lengthy lay-off through injury, Grealish has inspired a Villa revival of four straight wins, which has lifted the club into sixth place, a point behind Boro who have now lost three successive games.
Villa's latest victory came on the back of first-half goals from Anwar El Ghazi and the confident John McGinn, who has prospered from playing alongside Grealish, with substitute Albert Adomah notching Villa's third two minutes from time.
Boro's failure to score against Villa was hardly a surprise as they have now failed to find the net in any of their last six games against the Midlands club.
Villa made their intentions known in the first minute when McGinn, twice on
target in the midweek 3-1 win at Nottingham Forest, headed over the bar from
a swirling left-wing cross from El Ghazi.
But it proved to be a rare goal threat early on as the visitors defended solidly, notably through Daniel Ayala and Ryan Shotton.
It was a piece of sublime skill that eventually opened up the Boro rearguard in the 28th-minute as an astute pass from the industrious McGinn picked out El Ghazi who finished with a low left-foot shot past Darren Randolph.
Seven minutes before the break Boro should have been on level terms, only for George Friend to rifle a shot straight at Jed Steer.
It proved to be an expensive miss as in the 44th minute Villa doubled their lead, sparked by Grealish being flattened by John Obi Mikel.
The loose ball then ran into the path of McGinn to fire home a raking left-foot shot for his third goal in two games.
Although Middlesbrough managed to conjure more attacks in the second half the dominance of Tyrone Mings and Kortney Hause at the centre of the Villa rearguard effectively kept them at bay.
In the closing stages, Adomah was on hand to tap home an easy third goal in the 88th minute after Darren Randolph had parried a Neil Taylor shot, with Boro's latest defeat raising questions as to whether they can maintain a top-six spot.
Manager Tony Pulis was far from happy with his team's latest performance as he said: "It has been a difficult week after Wednesday's game (a 2-1 home defeat to Preston). The team was flat.
"I thought we slow and sluggish in the opening 20 minutes, and we gave away three shocking goals. They had five shots on target and scored three.
"It was a great ratio for them but the goals we conceded were very poor and it was unlike us.
"Having said that, Villa are a top side and they have the momentum at the moment.
"The international break has come at a good time for us. It will be a break to clear their heads and get going again. We have to do better than we did against Villa."
Opposing number Dean Smith said: "It was a really good performance. They defended in numbers and it was difficult to break them down as they shut down the middle of the pitch.
"But we never stopped trying to go forward and score, and in the end, it was a very good performance.
"There is momentum as we have put in some fine displays of late. Defensively we looked very solid, which had been our major problem this season, and from the front, our counter-attacking set the tone for the match.
"There is a spring in our step. There are eight games to go and there is now a smile on our faces."