Watford 2 Newcastle United 1: Martin Dubravka heroics can't stop third successive defeat
Benitez's side suffered a third successive Premier League defeat at a sun-baked Vicarage Road this afternoon.
Watford won 2-1 thanks to goals from Roberto Pereyra and Andre Gray. Ayoze Perez was on target for Newcastle, who remain 10th in the division.
However, the scoreline would have been worse had it not been for Dubravka.
Dubravka, signed on loan from Sparta Prague in January, made a series of first-half saves to keep his team in the game.
The 29-year-old hopes to join the club on a permanent basis in the summer.
United manager Benitez had made two changes, replacing Matt Ritchie and DeAndre Yedlin with Jacob Murphy and Javier Manquillo.
It started badly, and got worse before it got better.
An unmarked Roberto Pereyra opened the scoring in the second minute after being played in at the far post by Abdoulaye Doucoure.
Newcastle needed to slow the game down, but they kept giving the ball away, and Dubravka stopped shots from Pereyra and Troy Deeney.
Kenedy had a shot deflected wide at the other end of the pitch, but Watford, pressing high up the pitch, kept on coming.
Dubravka stopped a shot from Andre Gray with his legs, but he couldn't keep out a 28th-minute header from the striker after missing a cross from Pereyra.
United were indebted to Dubravka again later in the half after Paul Dummett brought down Gray in the box. The goalkeeper made a double save from penalty-taker Troy Deeney, and Newcastle went into the break 2-0 down.
Newcastle were better after the break. They took the game to Watford, and Benitez soon replaced Murphy with Ritchie.
United's breakthrough came in the 55th minute. Manquillo broke down the right and delivered a deep cross for Perez at the far post. The forward got ahead of his marker and beat Orestis Karnezis with a first-time shot.
The strike was his sixth in the league, and eighth overall, this season.
Newcastle, backed by 2,000 fans, went on to dominate the half. Benitez sent on Yedlin and Mikel Merino, but they couldn't force another goal.
And Benitez's players left the field knowing the damage had been done in the first half an hour.
WATFORD: Karnezis, Janmaat, Cathcart, Kabasele, Holebas, Pereyra (Deulofeu, 56), Capoue, Doucoure, Hughes, Gray (Richarlison, 79), Deeney (Mariappa, 62). Subs not used: Gomes, Britos, Sinclair, Femenia.
NEWCASTLE UNITED: Dubravka; Manquillo (Yedlin, 67), Lascelles, Lejeune, Dummett; Diame (Merino, 84), Shelvey; Murphy (Ritchie, 52), Perez, Kenedy; Gayle. Subs not used: Darlow, Haidara, Hayden, Joselu.
Goals: Pereyra 2, Gray 28, Perez 55
Bookings: Perez 41, Kabasele 58, Holebas 73
Referee: Roger East (Wiltshire)