It wasn't just the cheers of relief - as Bruno Fernandes' match-sealing second goal hit the net - that gave the game away.
The normally studious Ralf Rangnick had done so a couple of minutes earlier as Brighton pushed determinedly at the United goal looking for an injury-time equaliser.
As Graham Potter waved his arms to tell his team to go forward, Rangnick was equally decisive in telling his to go back.
After three successive games in which his side had held a lead, then lost it, the German did not want it happening again.
Following Cristiano Ronaldo's sensational opener, at home, and to opponents reduced to 10 men with over half an hour remaining following Brighton captain Lewis Dunk's red card, it was unthinkable.