The Argentine superstar found the top corner with a second half set-piece to clinch a surprise victory for the MLS side and give them a strong chance of progressing from Group A.

Inter Miami and Palmeiras have four points each, after the Brazilian side beat Al Ahly 2-0 earlier on -- the Egyptians like Porto have one point.

Samu Aghehowa's early penalty gave the Portuguese side the lead as they had the better of the first half and could have scored more.

However Telasco Segovia blasted Miami level and then Messi's free-kick helped them claim a noteworthy scalp, in a match many thought would be straightforward for Porto.

Co-owned by former England international David Beckham, Inter Miami played their first MLS match in 2020 and signed Messi in 2023, raising their profile significantly.

This was the first competitive victory for an MLS side over European opposition, in their second encounter after Chelsea beat Los Angeles FC earlier in the week.

"It's a huge joy, the whole team made a big effort, we worked really well," Messi told DAZN.

"It's a really important win for us and we have to enjoy it...

"You can see that we want to compete, and today we competed against a really good European team... we knew that today we were weaker, but we had our strengths."

Even with Messi, arguably the face of the tournament, the Mercedes-Benz Stadium was under half-full at kick-off, hamstrung by another 3:00 pm kick-off on a working day as it was for Chelsea's opener at the venue.

More fans entered throughout the game, keen to get a glimpse of the 37-year-old widely considered to be the game's greatest ever player, with nearly 32,000 present in the end.

Messi did not disappoint and was the game's outstanding player, involved heavily from the off.

The former Barcelona great clipped a dipping ball in behind for veteran striker Luis Suarez, who could only prod it at the goalkeeper.

Porto took the lead in the eighth minute after being awarded a soft penalty after a VAR review, as Miami defender Noah Allen made light contact with Joao Mario in the box.

Spain international Samu Aghehowa beat Oscar Ustari, who had saved a penalty in the goalless draw against Al Ahly, even though the stopper got a hand to his low effort.

Uruguayan striker Suarez, 38, might have levelled after Messi threaded him through on goal but, forced to use his weaker left foot, Porto goalkeeper Claudio Ramos denied him.

Javier Mascherano's side almost levelled through US international Benjamin Cremaschi after a charge forward from Suarez broke open Porto's defence, but Ramos made a smart near post stop to thwart him.

Maximiliano Falcon brilliantly headed off his own goal-line with Ustari beaten by Rodrigo Mora's effort to keep Inter Miami hopes alive.

Ustari denied Aghehowa and then scrambled the ball to safety as it rolled towards his net after Alan Varela crashed a shot off the upright and it hit him on the back, as Porto turned the screw before the break.

- 'Clutch moment' -

Inter Miami levelled right at the start of the second half, with Segovia blasting home Marcelo Weigandt's inviting cut-back to stun the Portuguese side.

Messi then sent Miami ahead with a goal all of his own making after 54 minutes.

The playmaker was brought down outside the area and dusted himself down before arrowing a classic Messi free-kick into the top right corner.

"(Messi) is a leader, he's the player he is, he's the greatest player in the world," Inter Miami forward Fafa Picault told DAZN.

"I had a feeling (the free-kick) was going in. That was a great goal, a great show of leadership and coming in a clutch moment for us."

Miami battled hard to keep Porto at bay and groans travelled around the stadium after seven minutes of stoppage time was announced.

Mascherano's players thew themselves in the way of shots in a way the former Argentine defensive midfielder would have done himself, and Inter Miami were eventually able to claim their much-craved victory.