Cheltenham Town pulled off an amazing raid at Boundary Park to claim a place in the FA Cup third round for the second season running.
It took a mighty effort from the Robins, who were under intense pressure throughout the second half, but they defeated their high-flying Division Two rivals with first half goals from Mark Yates and Paul Brayson before Will Haining set up a tense finish with a late Oldham goal.
The home side had 22 shots at goal to Cheltenham's six and won 13 corners to Cheltenham's three. But the only statistic that mattered was the number of goals.
Cheltenham manager Graham Allner was forced into two changes for the match with Grant McCann ineligible as a loan player and Martin Devaney suspended. Allner opted to include Yates in a strong midfield three alongside John Finnigan and Richard Forsyth. Hugh McAuley was also drafted in and given an initial free role on either side of the field.
It was the coldest afternoon of the season so far with supporters wrapped up in winter woolies and snow forecast for the Pennines overnight.
Cheltenham started with the biting wind in the favour but it was Oldham who began the game very positively.
Robins goalkeeper Steve Book gathered a weak shot from Paul Murray in the first minute but Latics should have gone ahead two minutes later.
Murray found David Eyres with an angled pass across the area and the 38-year old wide man crossed for Clyde Wijnhard, the former Ajax Amsterdam and Leeds United player. The pass sliced the Cheltenham defence right open but Wijnhard was off balance as he went for the ball and mis-kicked right in front of goal.
Book had to stretch to hold a back-header from Chris Armstrong in the 15th minute but only seconds later Cheltenham took the lead with their first shot at goal.
Paul Brayson was crowded out of getting in a shot by defender Julien Baudet with the ball going behind for a corner.
McAuley took it wide on the right and Mark Yates, making a late run into the box, met it with a firm header across goalkeeper Les Pogliacomi and inside his far post.
Oldham had barely recovered from that setback when they found themselves 2-0 down.
It was a simple enough move, Book launching a long kick down-field that was flicked on by Julian Alsop for Brayson to chase. He scurried through a gaping hole in the defence before planting a neat lob over the goalkeeper and in.
Wijnhard thumped a spectacular volley into the net in the 26th minute only to see the effort ruled out for offside, then the same player shot straight at Book from a position of space inside the area.
But there was another scare for the home side on the half-hour mark when McAuley crossed from the right and the Frenchman Baudet very nearly headed the ball past his own goalkeeper, his defensive header only just clearing the crossbar for a corner.
Oldham wound themselves into a much higher tempo in the minutes leading up to half-time and the Robins had to work extremely hard to stay with them.
Steve Book's goal had a remarkable escape four minutes before half-time in a very similar incident to the one involving Damian Spencer at the same end in the League game two weeks previously.
Eyres crossed from the left and Chris Killen, a £200,000-signing from Manchester City, met it with a header which whistled past Book, hit the crossbar and bounced down on the line. Michael Duff muscled himself in front of Wijnhard to head the ball clear for a corner then ended up in a heap in the back of the Cheltenham net.
Having survived that scare the over-worked Cheltenham defence found themselves defending a corner deep into first half injury-time. This time it was Murray who hit the crossbar from an acute angle, the rebound falling to Killen who scooped it over the bar.
As might have been expected, Oldham began the second half applying heavy pressure to the Cheltenham goal and won three corners in quick succession.
The defence survived them but there was another close call when Eyres, who had been booked for a foul on McAuley moments earlier, crossed for Killen in space 12 yards out. The New Zealander spun onto the ball but his composure deserted him and he could only stub a weak shot at goal, which John Brough was able to boot clear.
Latics boss Ian Dowie sent replaced a defender with a striker on the hour mark when he sent on Canadian international Carlo Corazzin in place of David Beharall. The Oldham formation at this point was something like 4-2-4 and the new man had a great chance almost straight away.
Killen picked him out with a cross from the right, Corazzin sent a header at goal but Book was out quickly to save at point-blank range.
The tide had been almost exclusively towards the Cheltenham goal for most of the second half but, in a rare attack, Brayson had Pogliacomi flying across his goal trying to reach a shot that brushed the outside of his left-hand post.
The in-swinging corners taken by Eyres from the right were causing all sorts of problems, especially with Wijnhard positioning himself in front of Book and preventing him from getting to the ball. Referee Graham Laws pulled the big Dutchman up on several occasions, much to the annoyance of the home crowd behind the goal, but mid-way through the second half another Eyre flag-kick was met by a booming header from Baudet. Book was beaten by it but Brayson, of all people, was on the line to head it away.
Allner sent on Williams for McAuley, who had been sitting tighter in midfield after the second goal, but the new arrival gave away a needless corner with his second touch.
From it, Murray raced in at the far post but could only direct his shot into the side-netting.
Substitute Wayne Andrews then missed the target when clean through on goal - blasting his shot over the bar - and in a last throw of the dice Dowie sent on defender Will Haining for John Eyre with Fitz Hall switched from defence to attack.
Ironically, though, it was Haining who finally broke through for Oldham seven minutes from time. A free-kick from Darren Sheridan was only partially cleared and Haining directed a header back beyond Book and in from 12 yards.
The closing stages - including four minutes of added time - were excruciatingly tense as Cheltenham coped with a barrage of pressure on their goal.
But they survived and can look forward to Sunday's FA Cup third round draw with anticipation once again.
OLDHAM ATHLETIC: Pogliacomi; Hall, Baudet, Beharall (Corazzin 59); Murray, Eyre (Haining 82), Sheridan, Armstrong, Eyres; Killen (Andrews 65), Wijnhard. Other subs: Miskelly, Duxbury
CHELTENHAM TOWN: Book; Howarth, Brough, M.Duff, Victory; Forsyth, Yates, Finnigan, McAuley (Williams 77); Alsop (Spencer 84), Brayson. Other subs: Griffin, Milton, Higgs
REFEREE: G.Laws (Tyne & Wear)
ATTENDANCE: 4,416