Porto's perfect start to their Primeira Liga campaign came to an end as they were held to a 0-0 draw by rivals Benfica in an O Classico devoid of clear-cut chances.
Jose Mourinho was aiming to find a response following Benfica's Champions League defeat to Chelsea in midweek, but they were unable to do so against the league leaders.
It took until the 33rd minute for either side to register a shot, with Heorhii Sudakov testing Diogo Costa from distance, which seemingly sparked Porto into life before the break.
Gabri Veiga then saw his attempt repelled by Anatoliy Trubin, with the first 45 minutes generating an expected goals (xG) total of 0.49 between both sides at Estadio Do Dragao.
The second half followed a similar pattern to the first, though Jakub Kiwior came close to turning into his own net just after the hour following a dangerous ball into the area.
Francesco Farioli looked to his bench with one last throw of the dice in the 90th minute, introducing 18-year-old Rodrigo Mora for his sixth appearance of the campaign.
And that gamble almost paid off, with the youngster cutting inside from the left and curling an effort towards goal, but his strike cannoned against the crossbar and behind.
Tempers between the two great rivals flared at the end following a needless challenge from Francisco Moura on Enzo Barrenechea, with neither side able to find a winner.
Data Debrief: Defences come out on top
Many were expecting fireworks in the latest instalment of O Classico given Mourinho's return to Benfica, but both teams were unable to provide an attacking spark in the final third during Sunday's contest.
Indeed, Porto edged the xG metric, generating a total of 0.66 from their eight shots, though only two of those were on target, compared to Benfica's 0.13 from their four shots.
But there were positives for both sides after the stalemate. Porto have now kept a clean sheet in each of their last four matches in the Primeira Liga. Their last longer run of games without conceding a goal in the competition was a stretch of five between March and April 2022.
Benfica, meanwhile, are undefeated in their last 23 games in the top-flight, last enjoying a longer unbeaten streak from September 2017 until April 2018.
