Arsenal were held to a 2-2 draw at Sporting in a Europa League round-of-16 tie that saw the lead change hands.
The Gunners made the trip to the Estadio Jose Alvalade aiming to return to North London with a healthy advantage ahead of next week's second-leg at the Emirates. However, it was actually the hosts who started the brighter of the two sides.
Sporting couldn't make their early pressure tell and as a result were duly punished, as William Saliba headed Arsenal in front just over 20 minutes in from a delightful Fabio Vieira corner.
Arsenal couldn't celebrate for too long given around 10 minutes later, Sporting were level with an almost identical goal. Goncalo Inacio rose highest to head beyond Matt Turner and thwart the Gunners' lead.
10 minutes into the second half and the game was flipped entirely on its head, with Paulinho putting Sporting in front after Turner could only parry an effort back into the danger zone.
The goal-scorer should have really put Sporting 3-1 up soon after, but fired wide with just Turner to beat. Within seconds Arsenal had drawn level in freak circumstances, Granit Xhaka's pass deflecting off of Hidemasa Morita and into the back of the net.
Mirror Football has identified six key talking points from an end-to-end encounter in Lisbon that ended with honours even.
Kiwior's first game
January signing Jakub Kiwior was handed his first minutes as an Arsenal player nearly two months after he first arrived from Spezia for £21million.
Those who have kept a keen eye on the Poland international's progression will know one of Kiwior's strongest traits is his passing ability and all-round technincal quality.
Despite his significant height, Sporting's first goal would suggest Kiwior still has some work to do in the air.
The debutant remained rooted to the spot when he really should have jumped to head clear the corner that Sporting equalised from. Kiwior's positioning could be questioned for the host's second as well.
Arteta rings out the changes
Given Arsenal are sitting five points clear at the top of the Premier League, some sections of the Gunners faithful may have been hoping to see Arteta field some fringe players for a Europa League game.
However, the boss has long made clear he expects his star players to be able to play three times a week and that is what is evidently required of the likes of Saka, Martinelli and Saliba to name just three.
With that in mind, the Spaniard did make six changes to the team that beat Bournemouth on Saturday and for context, the most changes Arteta has made between league games is three.
The tricky trip to Fulham that awaits Arsenal on Sunday in the league was clearly not in Arteta's mind given he named a very strong line-up for the trip to Sporting, with the aforementioned trio joining the likes of Zinchenko, Ben White and Granit Xhaka as players who will likely play at the weekend.
Vieira shines back home
In what was a scrappy affair at times with plenty of loose balls, it was Fabio Vieira who stood out among those in an Arsenal shirt.
He was often subject to boos and jeers from the Sporting crowd given his past ties to their rivals Porto, but Vieira didn't seem to let it phase him as he pulled the strings and was at the heart of all things positive for the Gunners.
Vieira has been questioned at times this season after his £35m switch last summer, but in Lisbon he looked much closer to the player that registered a goal or an assist every 66 minutes last season.
His assist for Saliba's header was delightful, with the perfectly weighted cross containing the right amount of height and curve to leave Sporting's defence rendered helpless.
If the Portugual under-21 international can produce the kind of form he does in his home country back in London, Arsenal could be on to a winner.
Martinelli leads the line
With Arsenal suffering from an attacking injury crisis and all three of Gabriel Jesus, Eddie Nketiah and Leandro Trossard ruled out, it was up to Martinelli to lead the line.
The young Brazilian put in a performance far more similar to the style of Jesus and Trossard than Nketiah, with Martinelli often dropping deeper than expected to come and pick the ball up from midfield while Arsenal's wide players stayed high.
Martinelli had two superb chances to get on the scoresheet, though with the first he would have been bette served by passing to Vieira who would have surely tapped into an empty net.
The second came after a sensational run, but a last-gasp intervention by Jeremiah St. Juste prevented a remarkable solo goal.
Overall, Arteta would have been encouraged by what he witnessed and it won't be a surprise to see Martinelli be deployed in the same role on Sunday.
Xhaka dons the armband
Granit Xhaka's infamous furious tirade at his own supporters now feels like a distant memory and therefore it is easy to forget it cost him the club captaincy.
However, with usual skipper Martin Odegaard ruled out of this clash with illness, Xhaka donned the armband and put in a spirited performance that highlighted his leadership qualities.
In the aftermath of Arsenal's opener, a melee ensued after Zinchenko felt he had been struck in the face. Xhaka was front and centre, fighting for his team-mates and protecting anyone in a red and white shirt.
A look a the second-leg
The result leaves this tie evenly poised ahead of the return leg at the Emirates in seven days' time.
With the away goals rule no longer, Sporting will be confident that they can spring a surprise in North London based on what unfolfed in Lisbon.
From Arsenal's perspective, they will harbour confidence that with home advantage they can get the job done, though some defensive frailties were certainly exposed and that will give Arteta plenty to think about.
