Leicester City recorded their first-ever Champions League victory at the King Power Stadium after Islam Slimani's header was enough to edge out Porto, whose late charge was not enough to knock the Foxes off their perch.
Slimani further endeared himself to Leicester fans in knocking in another fine header, rounding off a sweeping move from the Premier League champions that included a fine switch of play from Marc Albrighton and a pinpoint cross from Riyad Mahrez.
It was a fractured, tense game chock full of niggly fouls and bookings, but Leicester negotiated some intense pressure from Porto in the second period and emerged unscathed after an assessment of their Champions League credentials much more demanding than the one they received in Bruges two weeks ago.
In the end, they stand tall after two games with a maximum six points. In the group's other game, FC Copenhagen beat Club Brugge 4-0 thanks to an owngoal from Stefano Denswil and second-half strikes from Thomas Delaney, Federico Santander and Mathias Jorgensen.
While Leicester toast to a second successive victory in Europe, Tottenham got their first points on the board with a crucial and hard-fought 1-0 victory over CSKA Moscow in Russia. In-form Heung Min-Son clinched the winner after 71 minutes to guarantee three points for Mauricio Pochettino's men and deliver the result they needed after an opening defeat to Monaco at Wembley Stadium.
Son scored his fifth goal in four games, latching onto a perfect pass from Erik Lamela to convert past Igor Akinfeev. Spurs' Wembley tormentors Monaco, meanwhile, tasted their own home defeat as ex-Manchester United striker Javier Hernandez captured all three points for Bayer Leverkusen.
In the night's blockbuster match between Borussia Dortmund and Real Madrid, former Chelsea winger Andre Schurrle struck late to rescue a point for the Germans.Cristiano Ronaldo had opened the scoring for Zinedine Zidane's side before Pierre-Emerick Aubameyang levelled.
Then, Raphael Varane had looked to have wrapped up victory for Madrid before Schurrle popped up with a huge goal in the 87th minute to ensure the spoils were shared at Signal Iduna Park.
Sporting Lisbon meanwhile secured a 2-0 win over Legia Warsaw in the group's other tie, with former Fulham man Bryan Ruiz and Bas Dost both getting on the scoresheet for Ronaldo's former club.
Finally, in Group H, Juventus made light work of Dinamo Zagreb as they ran out comfortable 4-0 winners in Croatia. Miralem Pjanic, Gonzalo Higuain and Paulo Dybala all scored for the Serie A champions, while Adrian Semper's own goal completed the misery for the home side.
Juventus are top of the group, but only on goal difference after Sevilla saw off Lyon 1-0, Wissam Ben Yedder getting the game's only goal.
CSKA Moscow 0-1 Tottenham Hotspur
Monaco 0-1 Bayer Leverkusen
Borussia Dortmund 2-2 Real Madrid
Sporting Lisbon 2-0 Legia Warsaw
FCCopenhagen4-0 Club Brugge
Leicester City 1-0 FC Porto
Dinamo Zagreb 0-4 Juventus
Sevilla 1-0 Lyon