The Clarets secured their second victory of the Premier League season with a 2-0 result over the Hornets at Turf Moor.
Jeff Hendrick headed home a Steven Defour corner in the 38th minute before Keane netted his first top flight goal with a header of his own from a Defour cross five minutes into the second half.
After the game, Keane said: "That's our best performance of the season.
"We went in knowing what we had to do. Jeff Hendrick's goal settled us down and I managed to get a goal and from then we looked dominant."