Manchester United boss Ole Gunnar Solskjaer told BBC Sport: "It's always difficult to play Brighton. We have had good results and we've had to earn them the hard way - we managed to find a way in the second half.
"Mason [Greenwood] was mature. Today he was one of our brightest players. He was clean, he was tidy and he got the goal. It's a header inside the six-yard box and that's what we need more from Mason."
On picking Henderson over De Gea: "I've got two great keepers, two number ones. David de Gea spent a while back home and then he had internationals so he hadn't played for about a month. He'll definitely play football for us again."
Brighton boss Graham Potter told BBC Sport: "We contributed well in the game. We took the lead and were probably the team which carried the most threat in the first half - we just missed that final pass.
"Manchester United responded in the second half without creating too many chances. They scored from not too much.
"When it was live, I thought it was a penalty [on Welbeck] then I suppose it's the clear and obvious debate.
"If Mike Dean had given it, I don't think VAR would have overruled it. There's nothing we can do in the end. We're disappointed to come away with nothing."