#2 That Sergio Romero mistake
More than anything, it's Romero's absurd decision to prance outside his area and stop the ball with his left hand that cost United the most. To be fair, his defence left him with very few options and he chose the worst.
That Romero mistake came when the score was 1-1. Derby County now had the advantage and could calmly pass the ball out from the back and build their attacks and that's exactly what they went on to do.
If they could have held on for a bit longer, the game would have been sealed in normal time and the victory would have been even sweeter.
However, Lee Grant, former Derby player, put in quite a shift after coming on. He made a brilliant save to his left to start off proceedings in a red shirt and was unlucky to have conceded United's second after doing so well to stop the initial shot.