An entertaining game saw Rotherham United record another three points to move further up the table but they were made to battle all the way by the visitors.
It was an unchanged side that stormed straight on to the attack with a flowing move that ended with Steve Brogan having a shot blocked.
Town hit straight back on two minutes and they almost took the lead but from a corner, Fenton's header was cleared ff the line.
Back came the Millers for Danny Harrison to have a 25 yarder saved at full stretch by Gary Montgomery and he then had another long range effort that went just wide from 20 yards.
On eight minutes Marc Newsham went clear in the penalty area and he looked a certain scorer before he was brought down but Fenton escaped with just a booking as the referee gave a free kick just outside the penalty area. Brogan's free kick was blocked.
Andy Warrington then did well to block Logan and following a Rotherham corner Pablo Mills got in a header that appeared to be handled by a defender but the referee waved play on.
On 17 minutes Town almost opened the scoring when Newey hit a fine free kick from just outside the penalty area but Warrington superbly tipped the ball over the bar.
Back came the home team for Mills to head wide from a corner and then Newsham headed wide from a deep Brogan cross before Ryan Taylor had a shot blocked.
Warrington saved a 25 yarder from Toner before the deadlock was broken on 37 minutes when Newsham slipped the ball to Mark Hudson who netted his first goal for Rotherham with a well placed shot from a tight angle.
Just before the interval Town had a great chance to level matters but from a deep cross, Jones headed over the bar when he really should have found the net.
Grimsby opened the second half in a positive manner and Newey had a free kick punched out before he levelled matters on 52 minutes with Fenton heading home a Boshell corner.
But nine minutes later Fenton was sent off when he picked up his second yellow card for a foul on Hudson and that gave the Millers an incentive to push forward. O'Grady had a shot saved while Hudson fired over the bar before substitute Jamie Yates had a shot saved.
Mills was denied a goal when Montgomery superbly tipped his shot over the bar before the Millers went in front again on 77 minutes. Ian Sharps delivered a superb deep cross from wide on the right and O'Grady was on hand to knock the ball home.
Hudson was stopped by Montgomery and a Yates cross was too deep as United looked for the safety of a third goal but it wouldn't come and they had to defend resolutely in the last few minutes as Town looked to level matters.
But the home defence held firm and they pushed forward to win two late corners that brought no further reward before the whistle went to herald a well deserved home win.
Rotherham: Warrington, Tonge, Sharps, Coughlan, Brogan, Harrison, Mills, Hudson, O'Grady, Newsham (Joseph 88), Taylor (Yates 66). Subs: Annerson, Todd, Hurst.
Grimsby: Montgomery, Newey, Hunt, Fenton, Till (Bennett 46), Toner, Boshell, Logan (Bore 83), Whittle, Hegarty (Taylor 64), Jones. Subs: Clarke, Jarman.
Referee: Grant Hegley (Hertfordshire).
Attendance: 4,162 (747 away)















