Ajax will begin the defence of their Eredivisie title against AZ Alkmaar this weekend with striker Kolbeinn Sigthorsson warning it will be a tricky opener to negotiate for the champions. The Amsterdam club finished six points clear of Feyenoord last season to secure the trophy, and return to league action on Sunday looking for a similar outcome this time around. AZ had also been among the contenders last term but eventually settled for a fourth-placed finish, and Sigthorsson admits that is enough to make Ajax sit up and take note. \"AZ sell players every year but they always still have a good team,\" said the Icelander on www.ajax.nl. \"I find it amazing they only finished fourth last season having scrapped until the end. \"We had problems with them (the clubs played out two draws in the league). They know our game and are physically strong. I expect a good match. At any rate, we are happy with where we are at and have prepared well. Hopefully we can show that against AZ.\" Feyenoord\'s season began two weeks ago in Europe, although their UEFA Champions League adventure was short-lived with defeat to Dynamo Kiev in the third qualifying round. Coach Ronald Koeman insists that setback will have no bearing against FC Utrecht this weekend. \"We had two top matches across the two legs and that is something you cannot replicate during training,\" he said on www.feyenoord.nl. \"We are ready for FC Utrecht.\" PSV Eindhoven enjoyed a successful start to the campaign, winning the first piece of domestic silverware last Sunday by beating Ajax in the Johan Cruijff Schaal. Their league challenge begins on Saturday against RKC Waalwijk, and with a new man at the helm after Dick Advocaat took the reins from caretaker coach Phillip Cocu. PSV have strengthened their squad over the summer with the additions of Luciano Narsingh, Mathias Jorgensen, Zakaria Labyad and Mark van Bommel. And Advocaat is confident they can mount a serious title challenge, saying: \"With all due respect, PSV are not inferior to any opponent whatsoever, not even Ajax.\" The season gets under way tomorrow night when newly-promoted Willem II host NAC Breda at the Koning Willem II stadium. Fellow top-flight newcomers Zwolle begin their season with a trip to Kerkrade to face Roda JC, who will be looking to improve on their tenth-placed finish last term. VVV-Venlo came through the relegation play-offs to retain their Eredivisie status and will be aiming to start on a winning note at Heracles Almelo on Saturday. Sunday\'s matches see NEC Nijmegen travel to Heerenveen, FC Twente meet FC Groningen and Vitesse Arnhem - who qualified for the Europa League via the play-offs - face ADO Den Haag. From: FIFA