Harry Maguire's first goal of the season and Andre Onana's stoppage-time penalty save earned Manchester United a 1-0 win over Copenhagen in the UEFA Champions League, while Arsenal went top of Group B after beating Sevilla 2-1 in Spain.
Brazilian duo Gabriel Martinelli and Gabriel Jesus were on the scoresheet for the Gunners, who hold a one-point advantage over second-placed Lens.
How Man Utd's match unfolded
It was an emotional night at Old Trafford following the death of Sir Bobby Charlton on Saturday, with tributes paid before kick-off.
Sir Bobby Charlton, 1937-2023.
— Manchester United (@ManUtd) October 24, 2023
Forever loved ❤️ pic.twitter.com/92moDICImT
United struggled to impose themselves early on, and it was Copenhagen who came closest to scoring in the first half, with Diogo Goncalves volleying against a post.
Onana produced a brilliant save shortly after half-time to keep it goalless, while Christian Eriksen was denied at the other end as the contest sparked into life.
It was United who broke the deadlock in the 72nd minute, with Maguire heading in at the far post from Eriksen's cross after the Dane's initial corner had been cleared.
Copenhagen were awarded a penalty deep into stoppage time after Scott McTominay caught former Southampton midfielder Mohamed Elyounoussi with a high boot.
But Onana produced the most important save of his United career to date, getting a firm hand to Jordan Larsson's spot-kick to deny the son of former United forward Henrik.
Erik ten Hag's men sit third in Group A, a point behind second-placed Galatasaray.
United will hope to extend their three-match winning streak in all competitions when they host neighbours Manchester City on Sunday.
See: Man Utd report and line-up
Arsenal picked up their first away Champions League win since December 2016 with an impressive 2-1 victory at last season's UEFA Europa League winners Sevilla, securing only a fourth victory for the Gunners from 18 matches played in Spain.
How Arsenal's match unfolded
Arsenal started brightly and went close when Martinelli forced an early save from former Aston Villa and Norwich City goalkeeper Orjan Nyland.
The Gunners did take the lead in first-half stoppage time from a sweeping counter-attack, with Gabriel Jesus turning skilfully deep inside his own half and playing a through-ball to Martinelli, who raced through before rounding Nyland and tapping into an empty net.
Captain Martin Odegaard missed a glorious chance to double Arsenal's lead early in the second half, but he blazed his shot over the crossbar.
Gabriel Jesus did make it 2-0 on 53 minutes, though, cutting in from the left before whipping a stunning strike into the top-right corner.
Sevilla pulled a goal back through Nemanja Gudelj six minutes later, but Arsenal held firm to bounce back from their 2-1 defeat at Lens in Matchday 2 with a victory.
One potential concern for the Gunners is a hamstring problem picked up by Gabriel Jesus that forced him off during the latter stages.
"We’re really sad because he felt something in his hamstring, and he had to come off and I’m worried about that," Mikel Arteta told the club's official website.
Arsenal will be looking to extend their unbeaten start in the Premier League when they welcome Sheffield United to Emirates Stadium on Saturday.