Moussa Sissoko scored for the first time on his return to Watford as Derby were beaten 2-1 at Vicarage Road.
Ebou Adams fired the Rams ahead early on but that was cancelled out by a spectacular Vakoun Bayo effort in a first half that also saw Derby assistant manager Richie Barker sent to the stands.
Ex-France star Sissoko, in his second spell as a Hornet, struck in the 76th minute to complete a comeback that saw Watford maintain their 100 per cent start to the season. They have won all three Championship games plus an EFL Cup tie.
Derby opened the scoring in the second minute through Adams, who was making his first start since joining permanently from Cardiff having spent last season on loan.
Watford were caught out from a throw-in that allowed Kayden Jackson to cross from the right to where Adams was lurking just inside the box. The Derby man kept his poise to side-foot a volley between goalkeeper Daniel Bachmann and his right-hand post.
Watford bossed possession after that but the Rams pulled men back behind the ball to snuff out space. Mattie Pollock sent a long-range effort over and a header at debutant goalkeeper Jacob Widell Zetterstrom before fellow centre-back Francisco Sierralta headed narrowly wide.
Watford pulled level on the half-hour mark in spectacular style as Bayo peeled away from his marker to get in behind the Derby defence and volley Pollock’s long diagonal ball into the bottom corner, twisting his body in the air to get the perfect scissor-kick connection.
Tempers then flared in front of the dugouts after Edo Kayembe and Callum Elder clashed. Coaches and other players soon got involved, seemingly about a throw-in, with referee Geoff Eltringham showing a red card to Derby assistant manager Barker.
Zetterstrom dropped a clanger moments before the break by allowing Bayo to charge down a clearance but the Watford man could not find an unguarded net from a tight angle.
The second half was less exciting, with Watford again having more of the ball but Bachmann having to tip over a deflected David Ozoh effort, with the Hornets surviving a penalty appeal for handball from the corner that followed.
Adams almost put Derby back in front but his header from Nathaniel Mendez-Laing’s free-kick was too high.
Bayo headed over at the other end but Watford were not to be denied in the 76th minute. Substitute Liam Thompson managed to block Giorgi Chakvetadze’s shot after good work on the right from Hornets replacement Kwadwo Baah but Sissoko was on hand to lash in the rebound.
It was the 35-year-old’s first Watford goal since March 2022, when he scored against Arsenal in his one previous season with the Hornets, which was followed by two years at Nantes before manager Tom Cleverley brought him back on a free in July.
Sonny Bradley headed at Bachmann in stoppage time as Watford held on.
