Barcelona boss Ernesto Valverde believes Manchester United are back on the up - and would not want to face them in this year's Champions League.
Neymar's first-half strike was the difference in the 1-0 International Champions Cup win in Washington, although Barca's first-half display perhaps deserved more.
David De Gea produced a string of fine saves to thwart Barca's ever-impressive attack, although United's overall display and recruitment power makes Valverde wary of Jose Mourinho's resurgent United.
"Obviously it hasn't been well lately, but I mean they won the Europa League," the Barca head coach said.
"This year they are going to be in the Champions League. Their presence by itself is impressive. They impress.
"I think they are going to be a really hard team to beat.
"For me, they are contenders to win and they are going to be hard to beat in the Premier League and the Champions League.
"I wouldn't want to face them in the Champions League."
United improved as the match wore on, thanks in no small part to Barca's sweeping half-time changes.
Neymar was among the 10 players taken off at the break, having added to his brace in the pre-season defeat of Juventus. The Brazil forward has been strongly linked with a move to Paris St Germain, but Valverde brushed aside such talk.
"Neymar was very happy talking to his Manchester United friends outside the locker room just right now," he said. "He is still with us.
"Concerning the game, I am happy with the performance and I am happy that we won against a powerful team such as Manchester United.
"In the first half, I think there was a high rhythm in regards to both teams having chances in both boxes.
"It is clear that even though it is a friendly, both teams wanted to win tonight."
Meanwhile, Mourinho returns home in a positive mood, having been impressed by his team's improved second-half display against Barcelona and "special" player Paul Pogba.
"I think for the crowd it was good," Mourinho said after 80,162 saw the Reds' first defeat of the tour. "I think in pre-season it is important also to play for that.
"When you come to the US and you have a stadium with a few thousand very enthusiastic (fans), this is what they want - they want Messi, Neymar, Pogba, they want the best players to show what they are. I think it happened. First half was 1-0 but could be 2-2, 3-2, 2-3 because lots of chances, an open game. We didn't defend well, I was not happy with the way we were defending, but that's pre-season.
"In the second half, lots of changes for them and lots of changes for us, but both teams played for the result in spite of it being a friendly and the result not being the most important thing."
Mourinho was especially pleased with the performance of world-record signing Pogba. The France midfielder was particularly impressive in the first half and, while there remains an overall gap to the likes of Real Madrid and Barca, the United boss believes they have a player in the same bracket as Messi, Neymar and Co.
"Messi and Neymar, there is only one: one Messi and one Neymar, there are not two," he said.
"And Suarez, (Andres) Iniesta, (Gerard) Pique, and (Cristiano) Ronaldo, (Gareth) Bale, (Luka) Modric and Toni Kroos - there is only one, so they can only be playing for a club and not for two clubs. But I have to say one of my players today, Paul Pogba, he showed the level. He showed that he belongs to that level."