With the top two slipping up this weekend, when leaders Twente Enschede were held to a goalless draw by RKC Waalwijk and second-placed PSV Eindhoven lost 3-1 to PEC Zwolle, Ajax were able to capitalise despite ending their match with 10 men.
The victory literally brought the house down as there were dramatic scenes in the dying minutes when substitutes and coaches ran on to the pitch to avoid being covered by a huge amount of snow that suddenly crashed through the stadium's roof.
Fischer's Danish compatriot Eriksen added a third goal after 62 minutes when a 20-metre free-kick surprised Mulder at the near post.
"Our efficiency was the basis for this win, but we were much too sloppy in possession of the ball despite all the space we got," Ajax manager Frank de Boer told reporters.
"In matches like this... you can't afford to make the mistakes we made," Feyenoord manager Ronald Koeman told reporters.
"The 3-0 scoreline is a bit flattering as we had our moments and could not convert a penalty."
