This appears to have been a night shaped by one moment at each end.
That is often the difference in these ties. A Championship side can drag a Premier League opponent into an uncomfortable contest with intensity, direct running and home support. But if the top-flight team survives the big scare, its extra composure usually tells in the closing stages.
For Willock, a late winner in a cup tie would feel significant beyond the result itself. He has long looked like a midfielder capable of changing games with late runs, energy and directness. When Newcastle are at their best, they get goals from midfield as well as from the forward line, and that makes them harder to contain.
A contribution like this could also matter in the battle for minutes. Cup matches are often where squad players rebuild rhythm, force selection questions and remind the coaching staff of their value ahead of a crowded run of fixtures.
For Newcastle, progress in this competition matters. The club has spent the last few seasons trying to build depth, expectation and consistency, and cup runs are part of that next step. They test rotation, mentality and the ability to win without complete control.
The next point of focus is simple: whether this result becomes a springboard. Another round brings another chance to build momentum, while Millwall can take encouragement from pushing higher-level opposition so close on their own ground.