The Blaugrana backed up their 1-0 win at Old Trafford with a 3-0 success at the Camp Nou, with Messi on the scoresheet twice in the first period and Philippe Coutinho making the game safe after the break.
"It was spectacular," said the forward. "This is who we are. We were cold and nervous for the first five minutes. I don't know why, but then we took control."
United were the stronger side in the initial stages, before the tempo of the game slowed and Barcelona were able to get a tighter grip on the contest. From there, Messi was able to work his magic in the final third.
While his second goal came after a clanger from David De Gea in the United goal, Messi's first was marvellous, as he latched onto a loose ball, nutmegged Fred and fizzed a low shot beyond De Gea.
It's a goal that is well worth another watch (U.S. only):
Per OptaJose, it's been a while since Messi was on the scoresheet at this stage of the competition:
"I was lucky [on the first goal]," said Messi afterwards. "The second I had even more luck. But the important thing is that we achieved our goal of reaching the quarter-finals, which we hadn't for a long time."
Messi was also asked about the prospect of Barcelona landing another treble, as they are in pole position to win La Liga and into the final of the Copa del Rey. He said the team are taking things "step by step, little by little."
Having struggled to have his usual influence in the first leg against United, Messi was exceptional in the second. Not only did he net the first two goals on the night, he toyed with the Red Devils defenders with his sharp movement and passing skill (U.S. only):
Squawka Football provided the numbers behind yet another masterful performance from the Blaugrana icon:
Former Barcelona striker Gary Lineker paid tribute to the Argentina international:
Although this Barca side is not as fluid or free-flowing as some we've seen in recent years, manager Ernesto Valverde has made them a difficult team to beat. That robustness should serve them well in this competition, with even tougher challenges to come in the semi-finals and potentially the final.
In addition, the Blaugrana are blessed with Messi, and at the moment he is relishing taking on a huge chunk of the team's attacking responsibility. If he continues to excel from the strong foundations Valverde has helped put in place, Barcelona will be tough to stop in any competition this term.