Watford beat Luton 2-0 at Vicarage Road on Sunday to boost their Championship play-off push and leave their bitter regional rivals rooted to the bottom of the table.
The Hornets slumped to a painful 3-0 loss at Luton in October, but they avenged that result with a comfortable victory on home turf.
Tom Dele-Bashiru's early penalty and Edo Kayembe's tap-in put Watford in control before halftime.
That was enough for Watford to condemn Luton to a ninth defeat in 12 league matches.
Matt Bloomfield's men are five points adrift of safety and have gone 13 games without a win in all competitions
Bloomfield, hired from Wycombe to replace Rob Edwards in January, has been unable to revive the Hatters, who are facing the nightmare scenario of relegation from the Premier League to League One in just two seasons.
Watford, who had lost their last five home games, moved up to ninth place, three points off the last play-off place.
They took the lead in the 11th minute when Luton keeper Thomas Kaminski came off his line to claim the ball but only succeeded in upending Watford's Mamadou Doumbia.
Once Luton's protests had been waved away Dele-Bashiru made no mistake from the spot, slotting low into the bottom corner.
Tom Cleverley's side doubled their advantage in the 23rd minute.
Giorgi Chakvetadze showed impressive technique to evade Amari'i Bell's challenge down the left flank and, as Kaminski came out, he squared for Kayembe to finish from close-range.