Neil Harris' substitutes paid off on Wednesday night at The Den as Millwall advanced to Round Three of the Carabao Cup with a topsy-turvy 3-2 victory over Plymouth Argyle.
Jamie Ness put The Pilgrims into a first-half lead, but Shaun Williams equalised from the penalty spot just after the hour-mark.
Freddie Ladapo, though, had other ideas and put Argyle back in the lead minutes later, however, Lee Gregory and Aiden O'Brien stepped off the bench to turn the game on its head and put Millwall into the next round.
Harris made seven changes from the 1-0 defeat at Rotherham United on Sunday afternoon, with Conor McLaughlin, Williams, Tom Elliott and Murray Wallace the quartet to keep their places.
Jem Karacan made his second Lions debut, whilst Harry Donovan, recalled from a loan spell at Dagenham and Redbridge, made the substitutes bench.
The game started as a quiet affair with the first action in front of goal not coming until the 12th minute as Fred Onyedinma looked to turn Karacan's cross home to no avail.
On 15 minutes Argyle came to life and perhaps should've taken the lead through Ness, but a combination of the Millwall defence and Ben Amos denied him.
Midway through the first half it was The Lions' turn to nearly take the lead, but Shane Ferguson's shot looped on to the top of the net via a deflection.
A huge shout for a Millwall penalty was turned down in the 28th minute as captain Williams was hauled to the ground inside the box, whilst Onyedinma got his head to the skipper's cross three minutes later but steered the ball wide.
On 41 minutes Plymouth took the lead. Freddie Ladapo forced Murray Wallace into heading the ball out for a corner and from that resulting kick, Ness headed home to open the scoring.
Five minutes into the second half Murray Wallace headed Ferguson's free-kick over the crossbar. The Lions began to rally and had an effort from Williams blocked, whilst the captain and Conor McLaughlin created a good opening on 55 minutes but the latter's cross was deflected into the arms of Matt Macey.
The Pilgrims were struggling to get out of their own half but Millwall could not make the pressure pay - Onyedinma having a shot deflected on 57 minutes, whilst neat work from Elliott was undone following a poor cross minutes later.
Harris brought on Jed Wallace just after the hour-mark and that led to The Lions levelling proceedings, as a ball forward set Elliott on goal - he was pulled back by Ryan Edwards, who received a booking for his troubles, and Williams dispatched his penalty to Macey's right.
Parity, however, lasted all of three minutes as Ladapo broke away, shook off the attentions of Murray Wallace and slotted past Amos to nudge Argyle back in the lead.
Substitutes Jed Wallace and Lee Gregory combined with 20 minutes remaining as The Lions looked to draw level once more, but the latter headed wide from the former's cross. Mahlon Romeo swung over an inviting cross for Elliott one minute later, but the frontman got himself in a twist and poked the ball behind.
Jed Wallace curled in another Millwall cross on 77 minutes and Elliott rose highest, however the striker directed his effort wide.
Superb hold-up play from Gregory forced a corner with 10 minutes remaining but Jed Wallace's shot was blocked by The Pilgrims' defence. Substitute O'Brien, meanwhile, blazed well over.
Seven minutes from time Millwall were back on level terms as Gregory powered a Skalak cross home with his head. Williams then tested Macey from long range with the stopper having to tip over the crossbar.
One minute from time and with penalties looming The Lions took the lead for the first time in the game. A cross was swung in for O'Brien who prodded the ball home for the fifth goal of the game.
Gregory nearly turned Skalak's cross home late on into injury-time, but the encounter drew to a close shortly after with Millwall taking their place in the Third Round.
Millwall: Amos, McLaughlin (O'Brien 76'), Williams, Onyedinma (Gregory 67'), Ferguson, Romeo, Webster, Elliott, Karacan (J. Wallace 63'), M. Wallace, Skalak. Subs not used: Archer, Cooper, Morison, Donovan.
Scorer: Williams 64' (pen), Gregory 83', O'Brien 89'
Plymouth Argyle: Macey, Riley, Sawyer, Songo'o, Edwards, Ness, Sarcevic, O'Keefe (Carey 84'), Grant (Wylde 90+3'), Ladapo (Taylor 79'), Smith-Brown. Subs not used: Letheren, Fox, Grant, Wootton.
Scorer: Ness 41', Ladapo 67'
Booking: Edwards, Ness
Referee: Darren England
Attendance: 3,645 (635)