The main talking point after Reading's second successive away win was a bizarre own goal with virtually the last kick of the game.
It came when Grimsby midfielder Alan Pouton tackled Reading's substitute Darius Henderson 40 yards out and the ball flew past a bemused Mariners keeper Danny Coyne and under the bar to put the seal on a thoroughly depressing afternoon for the home side.
Reading's assistant manager Kevin Dillon said: "I've never seen a goal like it.
"Nobody seemed to know what was happening as to whether the goal had been given or not but as I saw it, it was an attempted tackle by Pouton on Henderson and the ball flew into the goal.
"Henderson is claiming the goal, but then he will claim anything."
But the game was won and lost in the first half when confident Reading, with a refreshing 4-5-1 formation, tore Grimsby apart and they could have no complaints about trailing 2-0 at the break.
Midfielder Andy Hughes opened the scoring in the 13th minute when he flicked the ball past Coyne after Tony Rougier had headed on and then in the 32nd minute man of match Nicky Forster burst clear, rounded the keeper, and slotted the ball into an empty net.
Grimsby, simply awful in the first half, tried to make a game of it after the break, but they did not have the skill to open up a well-organised Reading side who were clearly in no mood to give up their well won advantage.
The home support tried to raise their team but after a brief spell at the start of the second half in which Grimsby did try hard to press, the attempted comeback fizzled out and the game was dying on its feet before its remarkable conclusion