Ten-man Hull and Swansea both boosted their survival hopes with crucial victories, while at the same time compounding Middlesbrough's chances of escaping the drop and also putting Crystal Palace under pressure despite their recent fine form.
Boro, who had Gaston Ramirez sent off after 20 minutes, lost 4-0 at Bournemouth to leave them nine points from safety with just five matches remaining.
While the Teessiders were woeful, extending their winless run in the top flight to 16 matches, their relegation rivals were the opposite with Hull in particular showing they have the stomach for a fight.
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Hull, Oumar Niasse was somewhat harshly sent off for a foul on Watford's M'Baye Niang after 25 minutes, but they refused to buckle and Lazar Markovic's goal just after the hour was followed by a brilliant volley from Sam Clucas to extend manager Marco Silva's unbeaten personal home record to 41 matches.
It also ensured they remained two points ahead of Swansea, who easily got the better of a Stoke side who appear to be treading water in mid-table.
Fernando Llorente headed in Gylfi Sigurdsson's cross after just 10 minutes and Swansea got the stroke of luck they needed 20 minutes from time when Marko Arnautovic blazed over a penalty.
Less than a minute later Tom Carroll's long-range strike doubled the home side's advantage and secured a 2-0 victory.
Middlesbrough, by contrast, were never in their game on the south coast as Josh King and Benik Afobe gave the home side a 2-0 lead inside 16 minutes;
Ramirez's second yellow card, having received his first for diving, left Boro in dire straits and Marc Pugh and Charlie Daniels completed the rout midway through the second half.
Seventh-placed Everton's hopes of pressing home their claims for a shot at fifth foundered with a goalless draw at West Ham.
Burnley host Manchester United in the first of Sunday's two games, before Palace travel to Anfield to face Liverpool.
EPL Table | Premier League standings after Gameweek 34