Newport added Watford to their long list of recent cup scalps as they reached the fourth round of the Carabao Cup for the first time in their history with a 3-1 win over the Championship outfit.
Watford arrived at Rodney Parade unbeaten in their three outings this season, but conceded twice in the opening 30 minutes against the League Two outfit.
Having knocked out another Championship club – Swansea – in the opening round, their reward is another home tie next week against the winner of Wednesday night's clash between Morecambe and Newcastle.
Watford's new Serbian boss Vladimir Ivic sent out a team showing 10 changes from the one that drew 0-0 with Sheffield Wednesday in the Championship last weekend.
Veteran striker Glenn Murray, on loan from Brighton, was the only survivor.
The first chance of the night fell to Padraig Amond but the Irishman's header went over the bar.
A great corner from Matt Dolan just needed an end product to open the scoring, but nobody could reach it.
Moments later, though, Dolan had another chance to deliver a dead ball into the Watford box from a free-kick on the other side of the field.
Referee Charles Breakspear spotted some pushing and shoving in the penalty area as the ball was delivered and as well as awarding the home side a penalty, he showed Toby Stevenson a yellow card.
Newport maintained the pressure and skipper Joss Labadie needed no second invitation to hammer home a left-footed volley from the edge of the area to double the lead in the 28th minute after a defensive mix-up.
Newport stayed on the offensive and Amond should have made it three after Derek Agyakwa backed off him in a 30-yard chase. The Irishman hooked his left-footed shot just past the right post.
Watford made two changes at half-time and one of the newcomers, the Venezuelan international Adalberto Penaranda, halved the home advantage when he converted a penalty conceded by Liam Shephard.
The visitors were far more fluent after the break and pressed forward more, but they conceded again in the 65th minute when a wayward pass from Dan Phillips across his box found the Amond in acres of space.
As he moved into the penalty area he teed up his right foot and hammered the ball into the left corner of Bachmann's net to make the game safe.
Watford's night went from bad to worse in the 88th minute when Stipe Perica was sent off for a foul on Brandon Cooper.