Eberechi Eze scored against his former club as Arsenal beat Crystal Palace to extend their lead at the top of the Premier League table to four points.
Eze joined the Gunners in a deal worth £67m in the summer, and his winner came from another trademark Arsenal set-piece.
Declan Rice curled a free-kick into the area, which was knocked down by centre-back Gabriel, then Eze acrobatically fired the ball into the corner of the net.
Crystal Palace, who lost to AEK Larnaca in midweek, did threaten on occasion with Jean-Philippe Mateta battling against the solid Arsenal defence – but they did not trouble David Raya in goal.
Arsenal nearly doubled their lead in the second half when Gabriel hit the crossbar with a header and Bukayo Saka went close with a curled effort from the edge of the penalty area.
The win means Arsenal are now unbeaten in 10 matches in all competitions
Arsenal analysis: The type of performance that wins trophies
Arsenal came into this game with four wins from their previous four matches, in which they had not conceded a goal.
But on Sunday the Gunners did not start like a team who were top of the league and in such good form.
It took until about the 30-minute mark for them to have a shot on target through Leandro Trossard, and there had been some shaky moments at the back as loose passes and Mateta caused trouble during the first half.
Arsenal have been known for their threat from set-pieces for a while, and it was another excellent Rice free-kick that led to the opener and, ultimately, the match-winner.
The goal meant the Gunners have now scored 11 goals from set-pieces in the Premier League this season, two more than any other side.
Mikel Arteta has spoken repeatedly about why set-pieces and defending are important. In games like this against teams who pose a threat, being able to win when not playing at their best means Arsenal can keep grinding out the important points as they look to win the Premier League title.
Palace analysis: Effort from Eagles, but players tire
The Eagles are taking part in European competition for the first time this season, and this result will add to the concern about how the squad will deal with the extra midweek games.
Arsenal are a challenge for anyone, and the Palace players were visibly tired as the match reached the latter stages.
Oliver Glasner will have to think about how best to rotate his players while the fixture schedule for his team is so congested.
Palace are now without a win in four games in all competitions, but it has still been a solid start for them in the Premier League this season, with 13 points from nine games.
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DISCLAIMER: The Views, Comments, Opinions, Contributions and Statements made by Readers and Contributors on this platform do not necessarily represent the views or policy of Multimedia Group Limited.