Ole Gunnar Solskjaer hailed Canaries penalty hero Tim Krul – but insisted both spot-kicks the keeper faced should have been retaken.
Krul denied Marcus Rashford and Anthony Martial and the United boss referred back to a famous incident during the 2014 World Cup when Krul was brought on by Dutch manager Louis van Gaal in the final minute of extra time and saved two spot-kicks against Costa Rica as his side won 4-3 on penalties.
"He is actually one of the best in the world, Tim Krul, on penalties," said Solskjaer. "He is clever in his mannerisms as well. He should have been booked, probably, because he as staying away from the goal, but they should both have been retaken.
"He is off his line by a yard, the keeper, on both of them, so even though I didn't think the first one should have been a penalty, I thought they could have come back and given him (Rashford) another chance.
"It is like the six-second rule with the keeper, when he holds the ball in his hands. That was used for a couple of months and then it's out the window. This as well with penalties - he is a yard off his line. We looked at it for the first month and now it's gone."
United have now missed four out of six penalties awarded to them in the Premier League this season.
"Of course it is a concern," he said. "You think a penalty should be a goal than more than four out of six.
"We just have to keep practicing. Anthony scored a penalty on Thursday [in the Europa League], today he missed. Marcus missed one and then he scored.
"Good saves but still they should have been re-taken."
United's 3-1 win was their first away from home in the top flight since February.
"It has been, of course, too long, but it is great to have it done and of course this performance was the pleasing thing," he said.
"It is a difficult place to come to, but when we are as focused and concentrated and on the front foot as we were today we can beat anyone away from home.
"There's been a lot of talk about getting this away win - now we've won one in the Europa League and this one in the space of three days. I'm very happy and delighted with the boys."
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