Freedman opened the scoring in the 15th minute from David Hopkin's long throw. Ten minutes later another throw from Hopkin was missed by the Grimsby defence and Freedman shot into the roof of the net.
Within 60 seconds he completed his second hat-trick of the season after George Ndah's header rebounded off the bar.
Hopkin added the fourth, and seven minutes before the interval Ray Houghton took advantage of another defensive error to make it 5-0.
By contrast, another south London club, Charlton, saw their promotion push falter in a 3-0 home defeat by Southend, who thereby put themselves into play-off contention. Southend's first victory at The Valley for 60 years came with a header by Keith Dublin and powerful shots from Steve Tilson and Andy Thomson.Reuse content