Wes Hoolahan's 87th minute goal secured Blackpool a deserved win in this League One play-off semi-final first-leg.
Grayson's Blackpool have won eight successive games
The game only came to life in the second half with Blackpool going ahead after Shaun Barker headed in a corner.
Oldham lost Les Pogliacomi to injury and his replacement Alan Blayney kept his side in the game with a couple of courageous saves to deny Keigan Parker.
The home side drew level through an Andy Liddell penalty, but Hoolahan sealed the win after he broke clear.
Prior to Sunday Blackpool had won their last seven games of the season scoring 22 goals in the process, but Simon Grayson's side found Oldham an altogether tougher proposition in the first half.
Both sides proved too combative at times, with Richie Wellens' poor tackle on Hoolahan earning the former Blackpool midfielder a yellow card.
Not that Blackpool were above making illegal challenges and just before the interval Adrian Forbes was booked.
Blackpool had the best of the first-half chances, notably Parker, who drew a reaction save from Pogliacomi.
Just before the end of the opening half Porter briefly glimpsed goal, only for Paul Rachubka to get to the ball before the Oldham striker.
And Paul Warne should have done better when presented with an opportunity to shoot, but he skied the ball over the bar.
After the break Blackpool began to create a succession of chances as they took control of the game.
The Oldham defence allowed a cross from Forbes to reach Parker, but the former St Johnstone forward delayed his shot and Pogliacomi made the save.
Soon after Blackpool won a corner and Barker rose well to head the ball into the roof of the net.
Oldham suffered a further blow when Pogliacomi had to go off after he injured himself in collecting a low cross.
Pogliacomi's replacement Blayney was quickly into action, saving well from Parker.
Just past the hour Blayney threw himself at Parker's feet as the Scot spuned a fourth chance.
Against the run of the play Oldham were handed a route back into the game after Michael Jackson brought down Porter and Liddell made no mistake with the penalty.
But Blackpool continued to press forward and Hoolahan waltzed his way round Blayney before sidefooting the ball home.
Oldham had a late penalty appeal turned down as Blackpool held on for the win.
Whoever wins this semi-final will meet the victors of the tie between Nottingham Forest and Yeovil.
Oldham manager John Sheridan:
"We'll be going there to try and win the game.
"I've told the lads, and the fans to stay positive. I still think we can go there and win it.
"We just weren't at the races in the second half. They upped the tempo and we didn't."
Blackpool manager Simon Grayson:
"In the second half we showed what we're about.
"We got the ball down, passed and created numerous chances and on another day the tie could have been all over.
"There's still a lot of work to be done, but full credit to the players, they withstood pressure at times and then played the way we know we can."
Oldham: Pogliacomi (Blayney 59), Eardley, Haining, Gregan, Charlton (Edwards 58), Liddell, Wellens, McDonald, Taylor, Warne (Glombard 65), Porter.
Subs Not Used: Roque, Rocastle.
Booked: Gregan, Wellens, Edwards.
Goals: Liddell 75 pen.
Blackpool: Rachubka, Barker, Williams, Jackson, Evatt, Southern, Forbes, Jorgensen, Hoolahan, Morrell, Parker.
Subs Not Used: Coid, Vernon, Fox, Burgess, Gillett.
Booked: Jorgensen, Forbes, Parker, Williams.
Goals: Barker 52, Hoolahan 87.
Ref: I Williamson (Berkshire).