Manchester United manager Ralf Rangnick was left cursing a change to the handball rule while his Middlesbrough counterpart Chris Wilder hailed the magic of the FA Cup as the 12-time champions suffered a shock fourth round exit on penalties on Friday, Reuters reports.
Rangnick was left puzzled by Boro's 64th minute equaliser scored by Matt Crooks after the ball had clearly hit Duncan Watmore's arm before he played the ball across goal.
That cancelled out Jadon Sancho's 25th minute effort, although United should have already been out of sight with Cristiano Ronaldo missing a penalty as well as other chances and Bruno Fernandes and Marcus Rashford also culpable.
In a tense penalty shoot-out, the sides could not be separated before Anthony Elanga blazed the 16th kick over the crossbar to send Boro's fans wild.
While Rangnick lamented his side's profligacy, he was understandably miffed by Boro's equaliser.
"How can it be accidental if he controls the ball up in the air with his hand? It was clear it should not stand but in the end I was really surprised it stood," Rangnick said.
"We conceded a goal which I don't understand why it stood. He controlled it with his hand. In the moment when they scored, it was clear that VAR would not allow this goal to stand."
The handball rule was tweaked for this season and now states "if an attacking player's accidental handball immediately precedes another player scoring, the goal will now be awarded".
Even Boro boss Wilder was surprised the goal had been allowed to stand after a VAR check
"We rode our luck and took our chances. The decisions that are made through VAR have changed since I left the Premier League -- I thought straight away it was handball," he said.
"I thought it would be chalked out and delighted it wasn't."
Former Sheffield United manager Wilder's main target this season since taking over in November is to get Boro into the playoffs and they are already up to seventh.
An FA Cup win at Old Trafford against a very strong United team will certainly do wonders for his team's confidence.
It also lit the fuse for a weekend of FA Cup action.
"We are delighted, the opposition will be wondering how they did not progress, it is the magic of the cup, we rode our luck, took our chances and took it to a shootout," Wilder said.
"You give yourself an opportunity to witness scenes like tonight, 10,000 fans coming down the road and going away happy.
"A fabulous night for the football club and why fans around the world enjoy the FA Cup. You cannot get any better than winning at Old Trafford on a Friday night."
To complete a miserable night for 12-time winners United, an electrical surge meant their stadium catering operation ground to a halt and no food was available for fans during the game.
"We sincerely regret the disappointment and inconvenience this caused fans," a statement read.
"All remaining hot and perishable food was given away for free to supporters as they left the stadium."
