Wilfried Zaha scored the only goal of the match to hand Crystal Palace a 1-0 win and in the process relegate Watford in their Premier League game played at Selhurst Park on Saturday.
The Eagles started the game on a high and could have grabbed an opener in the seventh minute. A decent cross was played into the danger zone and it fell to Ivory Coast international Marc Guehi whose header flew inches wide.
Five minutes later, Zaha managed to get into the danger zone, and received a fine pass but his feeble shot was easily collected by Ben Forster in the Hornets' goal.
Nigeria international Emmanuel Dennis was well guarded by the hosts but was let loose in the 27th minute, and almost capitalised on the chance. A good cross was played into the area and the Super Eagle positioned himself well ready to take it, however, goalkeeper Jack Butland denied him.
Hassane Kamara handled the ball in the danger zone, in the 30th minute, and after VAR review the referee pointed to the penalty spot. Zaha held his nerve to send Foster the wrong way.
Eberechi Eze and Zaha had half chances to get another goal for Patrick Vieira's side but they did not capitalise on them and the first half ended with one goal separating the teams.
In the 69th minute, the visitors suffered a major blow when Hassane Kamara was given his marching orders after a second bookable offence. The first card had come in the 16th minute.
The impressive Guehi was subbed in the 73rd minute for what seemed like an injury, and Tyrick Mitchell took his position for Palace.
With 10 minutes to go, Super Eagles captain William Troost-Ekong was also introduced by Watford.
In the last five minutes, both teams had chances but the best one fell to Ghana international Jeffrey Schlupp late into the match, after he received a good pass in the area, but failed to beat the goalkeeper.
The Hornets are now officially back in the EFL Championship with three games to spare. They are on 22 points and the best they can do is 31 points, three fewer than 17th placed Leeds United.