Supersub Poul Hubertz picked the perfect time to score his first League goal as he slammed home a 79th-minute winner to secure Millwall's first victory of the season.
Danish striker Hubertz had only been on the field for eight minutes, but that was all he needed to make his mark on proceedings as Nigel Spackman's battlers clinched three welcome points.
Fellow sub Filipe Morais despatched a deft free-kick, and although keeper Chris Howarth did well to parry Marvin Williams' effort, big frontman Hubertz stole in at the far post to thump the ball into the roof of the net.
The celebrations that followed were as much those of relief as delight, but no-one could take away from the fact that this was a thoroughly deserved victory for the home side.
Pitched against a big, strong Oldham outfit it was vital that Millwall stood firm - and that they did from the first minute to the last.
Millwall started brightly and twice tested the visiting defence in the opening 10 minutes. A great touch by Kevin Braniff found Neal Ardley with two minutes on the clock, but the midfielder's effort flew wide of the target before some slick pass and move play between Tom Brighton, Braniff and Derek McInnes created an opening for Ardley, who saw his shot curl a yard wide.
The lively Brighton continued to pose a threat down the left flank, and nearly scored the opener on 15 minutes, only to see his deflected free-kick superbly tipped over the bar by Howarth.
Marvin Williams dragged narrowly wide on 20 minutes and the hard-working Braniff fired straight at the keeper from another good move eight minutes before the break.
Oldham were unable to get any attacking rhythm going during the opening period, not least because The Lions chased, harried and made life difficult for them to try and do so.
Millwall continued to press after the restart and the introduction of Morais on 54 minutes nearly produced an instant return with the former Chelsea man's first touch - a fierce shot - blocked for one of 10 corners chalked up by the home team.
Spurred on by the home support, who played their part, Spackman's side finally made the breakthrough 11 minutes from time thanks to Hubertz's timely strike.
It took an equally timely interception from Zak Whitbread at the other end to clear the danger from Lewis Grabban's low cross, before the defender's piledriver was blocked at the other end.
Millwall kept their shape and discipline in the dying minutes, and could even have added to their tally with Hubertz denied and then Morais drilling a yard wide after picking up a neat flick from his fellow sub.

Millwall: Pidgeley, Ross, Whitbread, Elliott, Robinson, Shaw, Williams, McInnes, Brighton, Braniff (Hubertz, 71mins), Ardley (Morais, 54mins). Subs not used: Day, Hackett, Dunne.
Booking: Shaw (77mins)
Scorer: Hubertz (79mins)

Oldham Athletic: Howarth, Swailes (Wood, 84mins), Haining, Stam, Taylor (Tierney, 46mins), Liddell, McDonald, Wellens, Molango (Grabban, 61mins), Warne, Edwards. Subs not used: Smith, Rocastle.
Bookings: Wellens (77mins), Tierney (90mins)

Ref: C. Boyeson
Att: 7,455 (Away 287)