Watson's effort came in the same minute as his winning goal in the previous home game against Barnsley and ensured Forest would end the day as joint-leaders of the Sky Bet Championship.
Sabri Lamouchi made three changes from Tuesday's 1-1 draw at Blackburn as Chema, Tiago Silva and Joao Carvalho came into the side in place of Tobias Figueiredo, Jack Robinson and Sammy Ameobi.
Joe Lolley carved out the game's first real opportunity as he produced a strong run through the middle third, racing past two Brentford midfielders, but his well-hit strike was comfortably saved by David Raya in The Bees' goal.
The game was proving to be an open affair with plenty of space afforded to both teams and Brice Samba was called upon to make a decent save from Josh Dasilva after the Brentford midfielder had found too much of that space on the right-hand side of the Forest penalty area.
Forest were pushing for the opening goal and Silva came within a whisker of handing them a 34th-minute lead as he curled a superb 25-yard free-kick inches wide of Raya's right-hand post after Yuri Ribeiro had been brought down in a central position.
The visitors almost found the breakthrough in fortunate fashion in first-half stoppage time. Mathias Jensen's 30-yard free-kick took a massive deflection off the Forest wall but a wrong-footed Samba was able to shift his weight and get back across to make the save and ensure it was goalless at the break.
Watson had scored the opening goal in the 56th minute of the last home game against Barnsley and he repeated the feat this time around. A right-wing corner was sent deep to the back post, Joe Worrall headed the ball back across goal and Watson produced a sublime finish to crash the ball into Raya's net.
Forest were happy to invite Brentford on and try to hit them on the break and they almost did so on 72 minutes. Lewis Grabban latched onto a ball in behind The Bees' defence, held it up and laid it off to Silva inside the penalty area but his powerful drive whistled past the post with Raya beaten.
Streaming forward at every opportunity, Forest were sensing they could put the game to bed and Raya was forced into two low saves to prevent substitute Ameobi from doubling the lead, the second from a shot on the edge of the penalty area.
Brentford were forced to end the contest with only 10 men on the field as Sergi Canos limped off injured after The Bees had made all three of their substitutions and Forest saw the game out in relatively comfortable fashion to ensure they went into the international break in style.
Forest: Samba; Cash, Worrall, Chema, Ribeiro; Sow (Adomah 78'), Watson (c); Lolley, Silva, Carvalho (Ameobi 64'); Grabban (Mir 90')
Subs not used: Muric, Figueiredo, Bostock, Robinson
Goal: Watson 56'
Brentford: Raya; Henry, Jeanvier, Jansson (c), Dalsgaard; Mbeumo (Mokotjo 63'), Dasilva (Benrahma 63'), Norgaard, Jensen (Karelis 76'), Canos; Watkins
Subs not used: Daniels, Thompson, Pinnock, Clarke
Booking: Canos 35'
Referee: Dean Whitestone
Attendance: 27,596 (1,005 away)
