Porto was the side that upset Manchester United in the last 16 of the 2003/2004 Champions League. Having a 1-0 advantage after the first leg ( just like they did against MU) Porto hoped to dump out another English side, Arsenal, in this year's last 16 of the Champions League.

They defended well to keep Arsenal at bay for most of the match. In the 3rd minute Saka was hauled down but the referee Turpin waved play on. Arsenal managed to carry on with the attack but failed to score. Trossard crossed to White who headed it to the top of the net - but on the outside instead of from underneath 😂

In the 30th minute Pepe stopped what looked like a certain goal for Arsenal. Saka finds White down the right, he stands up a delicious cross to the far post where Havertz lurks .... and would have scored. Out of nowhere Pepe hurled himself backwards and managed to get his head to stop the ball from going into goal. 😮

https://www.eurosport.com/football/champions-league/2023-2024/arsenal-v-porto-uefa-champions-league-live_sto10058240/story.shtml

It was not until the 40th minute that Arsenal levelled through a beautiful goal. Skipper Martin Odegard collected a loose ball, found Trossard who returned the ball to Odegard. He beautifully retained possession to beat another defender while Trossard got into position.  

Porto had used the offside trap several times. Pepe who had earlier stopped a certain goal spoiled the trap by making Trossard onside. Trossard scored. 

In the 67th minute Trossard had the ball into the net again. Knowing that he did not commit any foul and was not offside, Trossard celebrated. The referee did not allow the goal. 

Pepe was under pressure from Havertz. The goalkeeper joins them and the 3  of them collide and falls down. Trossard clips the ball over the 3 of them into goal. 

The referee held that Havertz had fouled Pepe. Arsenal's manager, Arteta, protested  and was booked  by the referee.

A VAR check showed that Havertz did not push Pepe but he did pull Pepe's shirt. So the decision to disallow the goal is correct. 

Arsenal had chances to score a second goal to avoid having to play extra time but failed to convert those chances. 

Extra time was scrappy with both sides unable to score so a penalty shootout was needed. 

Both sides scored the first penalty. Wendell was on target for Porto in the second but Raya's fingertips pushed the ball to the post and it did not cross the line.  2-1  in favor of Arsenal. 

Arsenal scored both its 2nd and 3rd putting great pressure on Grujic who must score or else Porto will lose. It was almost a repeat of Wendell failed 2nd as Raya managed again to get his fingertips to the ball. However Grujic's shot was too strong and continued on into goal although it was slightly pushed. This kept the suspense up with the score at 3-2.

Declan Rice scored Arsenal's 4th so putting pressure again on Porto. Raya became Arsenal's hero by saving Galeno's shot. 

The 5th penalty was not taken by both sides as the 4-2 score cannot be overturned. 

With that Arsenal are through to the Q-final  of the ECL for the first time  since 2010. A 14 year wait. 

 For Porto it was so near and yet so far. 

They almost repeated what they did against MU, Just like against Arsenal, Porto came to England with a  1-0 home win. The lost the 2nd leg against MU also by 1 goal but with a 1-2 score instead of 0-1 against Arsenal. 

Because of the away goal they scored against MU, they were deemed victors. 

In the case of Arsenal, both legs ended with 1-0 wins for the home side so a  penalty shootout is required.