Fellaini scored his second goal with a close-range header from Rashford's free-kick early in the second half. Romelu Lukaku scored a late fourth - his 11th goal in 10 United games - by converting Anthony Martial's cross from closerange.
Florian Flecker gives Austrian side LASK lead in 14th minute with stunning strike; Darwin Nunez nets second-half equaliser from penalty spot before Luis Diaz turns in from closerange; substitute Mo Salah wraps up opening victory for Liverpool
The decision was a controversial one as Sadio Mane smashed the ball into Sissoko's arm from very closerange. Mohamed Salah stepped up and slotted the ball narrowly past goalkeeper Hugo Lloris after a lengthy pause.
Zlatan Ibrahimovic also had a goal harshly ruled out for a high boot on ex-United goalkeeper Victor Valdes, while the Spaniard twice blocked the United striker's shots from closerange in the second half.
Galeno should have put Porto ahead in the first half when he missed two sitters from closerange - first hitting the post then somehow putting an even better chance from the rebound wide.
City, who had 10 shots in the first 15 minutes, added their second when Sergio Aguero sublimely lifted the ball over home goalkeeper Sergio Rico from closerange.
Keidi Bare gave Diego Simeone's side a first-half lead, heading home from closerange past Danny Ward. Robert Firmino scored from the spot on 83 minutes after Juanfran was adjudged to have fouled Divock Origi.
Raphael Varane scored the winner on the night at Old Trafford, heading home Aaron Wan-Bissaka's cross from closerange as United struggled to find their rhythm against an electric Wolves side.
The champions went ahead in the first half through Luis Suarez, who nodded in Ivan Rakitic's cross from closerange. On his 100th competition appearance the closest Lionel Messi came to scoring was when he hit the crossbar.
It had taken Sevilla just five minutes to take the lead as Wissam Ben Yedder tapped in from closerange after home defender Dejan Lovren fell over while trying to clear the ball.
Iheanacho, 19, added the third from closerange, then the teenager rounded the keeper to seal an emphatic win. Stoke conceded four goals for the third straight Premier League game.