Kai Havertz and Viktor Gyokeres both got on the scoresheet as Arsenal completed a perfect Champions League league phase by beating bottom club Kairat Almaty 3-2.
Needing just a point against the Kazakhstan minnows to seal top spot in the table, Mikel Arteta made 11 changes to his Gunners team - with Havertz given a first competitive start for Arsenal in 358 days.
It took just two minutes for the German to make his presence felt, providing the key pass for Gyokeres to fire in a second-minute opener. But Arsenal were stunned straight away from kick-off.
A long ball forward saw Kairat forward Jorginho held back by Riccardo Calafiori, who also returned from injury. VAR sent referee Urs Schnyder to the monitor and after the spot kick was awarded, Jorginho converted past Kepa Arrizabalaga.
But Arsenal were back in front and Havertz got a goal on his return, cutting inside on his left foot before blasting high into the net.
Arsenal could have extended their lead even further but Gyokeres missed two massive chances - including one sitter from under the crossbar.
But sooner or later, it was three and Havertz made his mark again - getting into space in the area to cross for Gyokeres, whose prodded effort was helped on again by Gabriel Martinelli on the goalline. VAR checked for offsides on Havertz and Martnelli but the goal was given after a lengthy check.
Arsenal took Havertz and Calafiori off at half-time to manage their minutes and breezed through the second half. Martin Odegaard had two headers saved while there was a feel-good factor when academy players Brando Bailey-Joseph and Ife Brahima made their senior Arsenal debuts at 17 years old.
Gabriel Jesus saw a late fourth ruled out quickly by the semi-automated offside and there was a late consolation for Kairat forward Ricardinho.
But it was a near-perfect night for Arsenal, who will play either Borussia Dortmund, Olympiakos, Atalanta or Bayer Leverkusen in the last 16.
More to follow.
Analysis: Havertz shows why he is so crucial
It was a night where Arsenal reminded everyone why they enjoy the Champions League so much. With Kairat opting not to play a low block - something few teams will task Arsenal with in the knockout stages - they had attacking space to run into and their creativity showed.
The star performer in that attacking triumph was Havertz, given only 45 minutes in his first competitive start in 358 days - but he reminded everyone why he is such a crucial component to this Arsenal attack.
Havertz played in the attacking midfield role normally taken by Martin Odegaard and he was the best player on the park in the first half, controlling matters despite barely playing for almost a year.
He created three big chances, which included two assists for Gyokeres and Martinelli's goals, before scoring himself in a finish that may have convinced a few that he had never been away at all. He also had the second-most touches in the opposition box behind Gyokeres, who benefited from having another presence at the top end of the pitch.
When Havertz plays, he has this ability to unlock Arsenal's attacking potential by bringing others into the game. He is also a physical presence that very few in the Arsenal frontline have, but he is also technically brilliant too.
With Gyokeres and Odegaard missing chances, both Arsenal players will have noted Havertz's return to action - with both of their places coming under threat now.
"I wouldn't be surprised if Havertz starts against Leeds," said Kris Boyd. After having to wait so long, Havertz's next chance may even come on Saturday.
When is the knockout phase play-off draw?
The Champions League knockout phase play-off draw takes place at 11am UK time on Friday.
When is the draw for the last 16?
The draw for the round of 16, quarter-finals and semi-finals takes place on February 27.
When are the knockout stages?
Knockout play-offs: February 17-18 and 24-25
Round of 16: March 10-11 and 17-18
Quarter-finals: April 7-8 and 14-15
Semi-finals: April 28-29 and May 5-6
Final: May 30 (Puskas Arena in Budapest, Hungary)
