The Blaugrana had to survive an early onslaught from United but they quickly grabbed control of the game thanks to Messi's strike after 16 minutes, where he capitalised on a mistake from Ashley Young before finding the back of the net.
Messi scored a first-half brace and Philippe Coutinho added Barca's third in a 3-0 win over United at Camp Nou on Tuesday, a result that sealed a 4-0 aggregate success.
"We know there's work to be done". "In the next few years it is going to be a massive effort to get to the level of Barcelona and these sorts of teams". It's a big week and we have to get ready for that week because (they are) three big games.
"We had to be fearless, we created two or three chances but unfortunately we just didn't have that quality to finish them off. Whenever he gets the ball around the box he will be decisive and unfortunately for us he was the victor for them".
The title in LaLiga Santander has already been wrapped up, and they will face Valencia in the Copa del Rey final, yet Europe's premier competition has eluded them in recent years, particularly at the quarter-final stage, but they are into the last four.
"It starts with the coaches and players, and with one or two additions".
Solskjaer felt United needed to display a fearless attacking mindset in the intimidating atmosphere, similar to the one that saw them overturn a two-goal deficit at Paris St Germain in the last 16 last month.
Ole Gunnar Solskjaer has sent Manchester United's executive vice-chairman Ed Woodward a message after the defeat to Barcelona. "I dont mind if we score the victor in the 93rd minute".
Solskjaer said: "That's unfortunate with goalkeepers".
"I think it's important when you make a mistake of that nature, in your home country, he's now an experienced player".
"The quality of their finishing was absolutely outstanding".
"The attitude was right, we were fighting against a good team and good players out there". How to Get UEFA CL 2018-19 Leg 2 of 2 Match Live Telecast on TV & Free Football Score Updates in Indian Time?