It came after Yannick Bolasie gave Alan Pardew's men the lead in the fifth minute, with a lethargic-looking Watford then struggling to make an impression on the Palace defence.
To make matter worse, Etienne Capoue was then taken off after a collision around the 30-minute mark, apparently suffering from a knock to his knee.
In the second half, Watford looked much livelier, pressing forwards with captain Troy Deeney scoring in the 55th minute – a goal that seemed to give the Hornets confidence.
But it wasn’t to last with Wickham scoring six minutes later and the Hornets' fate seemed very much sealed. Despite creating more opportunities to get themselves into the final third they simply could not capitalise.
Watford's Etienne Capoue lies on the pitch after sustaining an injury
Image credit: Reuters
Palace will face Manchester United - who beat Everton 2-1 on Saturday - on May 21 at Wembley
With rumours abound that Quique Sanchez Flores’ job is on the line after a less inspiring second half of the season, this could spell bad news for the former Valencia manager. Having managed no less than eight teams in 11 years, despite having done a pretty good job at Watford – who will stay in the Premier League by a comfortable margin – Quique ends the day in a much more precarious situation. He might not mind, however, if the rumours that Valencia want him back prove to be true.
MAN OF THE MATCH
Though he didn't actually score a goal himself, Wilfried Zaha put real pressure on the Watford defence making blistering runs into the area and looking consistently dangerous.