With 28 occasionally entertaining minutes elapsed, Watford's Gavin Mahon advanced and had yards of space into which he could play Marlon King. With the ball safely under control, King calmly rounded the prone figure of Palace goalkeeper Gabor Kiraly.
The hosts might have opened the scoring within seven minutes when Jobi McAnuff's cross, destined for Andrew Johnson's head and probably the Watford net, was diverted by Lloyd Doyley's header.
In similar fashion, the visitors' centre-back Malky Mackay would have had a tap-in six minutes later had Darren Ward not fashioned a desperate clearance. Mackay's team-mate Chris Eagles was then presented with a chance from 12 yards but he struck his shot high.
A clash between Foster's shoulder and Johnson's head saw the striker come off worse. What looked like an innocuous challenge saw Johnson replaced and, strangely, precipitated Palace's sudden recovery, as just four minutes later the Eagles were level. A pass by Tom Soares was destined for Jobi McAnuff but Jay DeMerit brought down the winger and Dougie Freedman levelled matters on the rebound after his spot kick was saved. Five minutes later, Palace took the lead in fortuitous circumstances. A throw-in by Palace was met by Jordan Stewart but the unlucky Watford left-back saw his header loop backwards and over Foster.
An uncomfortable night for DeMerit was capped off five minutes from time when he turned in Soares' cross past his own goalkeeper under pressure from Clinton Morrison.
Crystal Palace (4-4-2): Kiraly; Hall, Popovic, Ward, Boyce; Soares, Watson (Riihilahti, 86), Hughes (Leigertwood, 90), McAnuff; Morrison, Johnson (Freedman, 50). Substitutes not used: Speroni (gk), Reich.
Watford (4-4-2): Foster; Doyley, Mackay, DeMerit, Stewart (Bangura, 87); Eagles (McNamee, 84), Mahon, Spring, Young; King, Henderson. Substitutes not used: Chamberlain (gk), Chambers, Carlisle.
Referee: M Thorpe (Suffolk).