Midfielder Andre Gomes netted his fourth goal of the season in the 44th minute, concluding a dominant first-half display from the visitors, during which Paco Alcacer had two efforts disallowed for marginal offside calls.
Alcacer finally won the officials' approval when he doubled Valencia's lead after half-time and an Enzo Roco own goal followed by Nicolas Otamendi's injury-time strike ensured Nuno Espirito Santo's men pulled four points clear of Atletico Madrid in fourth ahead of the champions' encounter with Getafe.
Otamendi spurned a glorious chance in the second minute, steering wide from the centre of the penalty area after Elche failed to deal with Jose Luis Gaya's free-kick.
Alcacer then rounded Elche goalkeeper Przemyslaw Tyton after a slick attack but David Lomban got back to clear off the line.
Valencia's pressure continued and Alcacer was twice denied by the assistant referee's flag, but Gomes made sure their frustration would not last by completing a simple finish after Tyton kept out Feghouli's angled volley on the stroke of half-time.
The Portuguese turned provider 12 minutes into the second half, fizzing in a low cross for Alcacer to prod home.
Jonathas sent a rasping drive over in the 65th minute as Elche looked to respond but their fate was sealed shortly afterward when Roco turned Antonio Barragan's low centre into his own net.
Tyton saved smartly from Pablo Piatti is stoppage time but, from the resulting corner, Otamendi was given space to complete the rout.
