Groningen hit Feyenoord for six
Winger Dusan Tadic opened the scoring after just 45 seconds, Maikel Kieftenbeld netted a superb long-range effort and Petter Andersson added the third.
Leandro Bacuna, Virgil van Dijk and Suk Hyun Jun completed the rout in the second half.
Ronald Koeman's Feyenoord, who suffered their biggest defeat one year ago when they lost 10-0 at PSV Eindhoven, earned praise last week following a 1-1 draw at Ajax but were knocked out of the Dutch Cup on Thursday by second division Go Ahead Eagles Deventer.
Feyenoord slipped to sixth with 18 points after 11 matches, 10 behind AZ Alkmaar who stretched their lead to six points after a late 1-0 win at Heracles Almelo.
Alkmaar dominated the match but had to wait till the 88th minute before youngster Adam Maher broke the deadlock after beating three opponents in the penalty area.
PSV and Twente Enschede, who drew 2-2 on Saturday, are second and third with 22 points and Ajax ended a winless streak of five matches by winning 4-0 at Roda JC Kerkrade.