Ghanaian players Jordan Ayew and Albert Adoma featured as Aston Villa edged within three points of the Championship play-off zone after leaving it late to beat manager Steve Bruce's old club Wigan Athletic.
Steve Bruce's men were frustrated by the visitors and looked to be heading for their 11th draw of the campaign
That was until two minutes from time, when Grealish finally broke Wigan's resistance with a stunning goal.
The 21-year-old picked up a loose ball before curling an effort past Jussi Jaaskelainen and into the top corner.
Grealish's goal sparked jubilant scenes at Villa Park as the hosts climbed into 12th.
Wigan showed little attacking threat throughout the clash and could have been behind inside 10 minutes as Jordan Amavi went close.
A last-gasp intervention denied Jonathan Kodjia on the stroke of half-time as the two sides went in goalless.
Villa continued to threaten but couldn't find a way past the resolute Wigan defence until Grealish's moment of brilliance.
Jordan Ayew played full throttle of the game, while Albert Adomah was subbed off in the 70th minute.