Tonge lashing for Watford as Rams edge clear
Tonge scored early on and Chris Porter added the second 14 minutes from time.
Watford improved second half and Derby suffered a few jitters.
Stephen Bywater was forced to make a couple of important saves and the Rams' play became a little ragged until Porter found the net and made sure the three points were in the bag.
Derby made one change to the team beaten by West Bromwich Albion.
Fit-again Rob Hulse came in for on-loan forward Gilles Sunu who dropped to the bench. Sunu only returned from international duty with France Under-19s Friday afternoon. Hulse partnered Porter up front.
Watford included two players who have had loan spells at Derby in recent seasons - striker Danny Graham and midfielder John Eustace.
A minute's applause was held before kick off for Macclesfield Town manager Keith Alexander who died this week aged 53. Both teams wore black armbands.
Stephen Pearson was fouled twice in the opening minutes, and then won a corner. Robbie Savage took it, Paul Green helped the ball back in and Hulse's header was easily held by Scott Loach.
A neat passage of play ended with Pearson beating his marker. The Scot pulled the ball back invitingly for Green's whose effort was pushed away by Loach.
Derby's bright start was reward when they took the lead after 12 minutes.
Green carried the ball across field and laid it off to Tonge. Nicky Hunt went on the overlap down the right but Tonge cut inside on his left foot and fired a shot from 25 yards high past Loach. The ball bounced down off the underside of the bar and then into the net.
The fine strike was Tonge's first goal for the Rams.
When Watford threatened, Stephen Bywater saved at the feet of Graham and minutes later Graham was fouled by Dean Moxey who was shown the first yellow card of the afternoon.
Hulse, cleverly found by Savage, broke but his curling centre only found Pearson on the left. He picked out Green whose shot sailed high over. Derby were on top for much of the half but there was a warning for them six minutes before the break when Jay DeMerit got his head to a free kick and Graham flicked the ball just over.
Jon Harley fired straight at Bywater from a free kick given by fussy referee Graham Horwood who left players, coaching staff and fans scratching their heads with a number of his decisions first half.
Watford started the second half with greater purpose than they had shown in the first and Bywater dived low to his right to deny Henri Lansbury with a good save.
There was an edginess about Derby as they struggled to settled after the break and an awful mistake by Moxey did not help matters.
His poor header fell well short of Bywater and Lansbury was in. Rather than lob the goalkeeper, the Watford midfielder tried to take the ball inside Nicky Hunt who made a vital tackle.
Derby needed a lift and got one when DeMerit's error led to them going two up after 76 minutes.
DeMerit dithered and Porter pounced to run away from the defender and coolly finish low past Loach from 15 yards for his second goal in as many games and his third of the season.
More strong running from Porter set up Green whose shot from the edge of the area went over.
When called on, Rams centre-halves Shaun Barker and Jake Buxton continued to defend solidly but when a ball from Lansbury drifted over the back four, Bywater did well to deny Graham.
DERBY COUNTY: Bywater; Hunt, Barker, Buxton, Moxey; Tonge (Anderson, 81), Savage, Green, Pearson; Porter (Martin, 89), Hulse (Davies, 75).
Other subs: Deeney (gk), Leacock, Pringle, Sunu.
WATFORD: Loach; Mariappa, DeMerit, Taylor, Doyley (Henderson, 82); Cowie, Eustace, Lansbury, Harley (McGinn, 77); Graham, Helguson (Hoskins, 71).
Other subs: Lee (gk), Jenkins, Bennett, Hodson.
Referee: G Horwood (Bedfordshire)
Attendance: 29,492 (away fans 776)
