Starting 2-0 down against a team as fundamentally solid as Thomas Tuchel's Chelsea is a daunting prospect for any team. You wouldn't know it though from the way Porto began the second leg of their UEFA Champions League quarterfinal.

They started attacking from the opening whistle and were convincing with it. This wasn't a desperate performance – in fact, it suggested that Sergio Conceicao's team may not even be capable of such.

Kai Havertz was floored in the opening five minutes from a harsh tackle by the dastardly Pepe. Besides that, this was a more intense version of the well-disciplined football Porto have displayed throughout the tournament.

They quickly established dominance over possession and began threatening the Chelsea goal. The pressure was perhaps unexpected as goalkeeper Edouard Mendy almost sliced it to Jesus Corona while trying to make a clearance.

If there was a weakness on display, it was that Conceicao had lined up in the same 4-3-3 formation and with the same swarming tactics as in the previous leg. It didn't work last time due to Chelsea's solid defense and, by the end of the first half, it became clear that executing the same plan, only at a faster pace, wasn't going to make much of a difference.

Chelsea already had the sizeable score advantage so were willing to sit back and let Porto push forward. This then gave them space to hit on the break. Jorginho and N'golo Kante in the center of the midfield found themselves orchestrating these dashes that were later picked up on overlapping runs by Ben Chilwell on the left and Reece James on the right.

The front three, ring-fenced as attackers, were largely absent from the play. The narrative has been that the new hires from the Bundesliga have been misfiring. However, even when Timo Werner and Hakim Ziyech are benched and replaced with Mason Mount and Christian Pusilic, Chelsea are goal-shy.

As with the first game, this was an equal game. Chelsea's goals then came from Porto mistakes, and all the best Porto chances came this time from Chelsea. An occasional loose ball was stolen and aimed goal wards. Jesus Corona almost broke through with the same cheeky turn that worked for Mount last week, only he snatched at the ball and sent it flying.

By the second half, the match had settled into a rhythm. With 30 minutes left, the tie was practically out of reach for Porto, yet they never gave up their professionalism or drive. On the one hand, when a game plan is being stymied so often, a team needs a definite plan B. On the other, it got them through the Group Stage, Juventus, is doing extremely well in Liga NOS and would have probably worked against a sloppier team.

Mehdi Taremi, Porto's top striker, came on and instantly made an impact. Mendy had to dive to save a header. His arrival late also answered the questions as to why he didn't play for the first hour of the game; he was subbed in for midfielder Marko Grujic, and it upended Porto's style of play.

Without Grujic as a deep midfielder, there was a massive gap between the back four and everybody else. Any time Chelsea got the ball, they had acres to work with and would have likely put plenty past Porto if they weren't already two goals up.

In the 90+4th minute, deep into added time, Taremi got a wonderful goal – maybe the best of the Champions League so far this year. Out of nowhere and with less than 60 seconds remaining, Nanu crossed it in from the right, and Taremi leaped into the air and nailed a bicycle kick into the far corner. In the replay, the ball was clearly at head height when Taremi hit it.

Chelsea won 2-1 on aggregate and were deserved winners. They will be a legitimate challenge to whoever they draw next. Commiserations to Porto; if that team can be kept together and bolstered, they'll be welcome regulars to the tournament.