This was a reminder both of Arsenal's new-found squad depth, but also that those players knocked down the pecking order by the summer's lavish recruitment drive should not be written off just yet.

Just as this game appeared to be drifting towards goalless stalemate, the visitors flung on Gabriel Martinelli -- a player presumably stung at seeing his starting place at the club threatened by new signings -- and, less than a minute into his appearance off the bench, the Brazilian made his mark.

Neither Andoni Gorosabel nor Aitor Paredes could keep up with the substitute on the sprint, with his finish fired through Unai Simon to prise Athletic Club apart.

As if to labour the point, Martinelli went on to set up his fellow substitute Leandro Trossard three minutes from time to secure an impressive win and ensure Arsenal are up and running in this season's Champions League.

This had not been a straightforward evening for the Premier League side. The locals had been whipped up into a frenzy in the Estadio de San Mames for a first Champions League fixture in 11 years, with Arsenal initially struggling to exert any kind of control and their midfield bypassed too easily. There was little pattern or cohesion to their play through those early stages.

Yet, once they had weathered the storm, they arguably created the better opportunities. Eberechi Eze was denied an opener by Gorosabel's timely challenge, with Viktor Gyokeres heading wide moments later. The Swede might have punished Athletic early in the second half, too, only to nod a Declan Rice free kick wide.

As it was, Arteta's team would make the breakthrough once Gyokeres had departed the turf. Here, Art de Roche dissects the key moments in Bilbao.

Speaking to TNT Sport ahead of the game in Bilbao, Mikel Arteta had said: "In this moment, if you don't have players who can do different things, it's not going to be enough." All it took was 36 seconds for Martinelli to demonstrate that Arsenal are well stocked on that front.

Eze started again on the left wing for Arsenal, and performed well enough on his European debut, but the England international has very different qualities to Martinelli. While on the pitch, Eze's short passing, dribbling and interchanges with others took Arsenal up the pitch, while he also won the joint-most tackles in the game at the point of being taken off (three).

With the game becoming more stretched, however, Arteta recognised the need for more pace and was rewarded instantly.

Martinelli is at his best when he is running into space. That is not new. Last season, that is how he scored the winner away to Real Madrid in the Champions League quarter-finals. The year before, that is how he put Arsenal ahead away to Sevilla in the group stages.

For his goal, the presence of mind he demonstrated to head the ball initially was instinctive and expertly executed, as was his touch to set the ball up before finishing.

The Brazilian's assist for Trossard was just as impressive as, once again, he played to his strengths. After receiving the ball, all he had in mind was to get to the byline and find a team-mate.

That the team-mate was Trossard -- the man whose flicked pass had sent Martinelli away for the opener -- would have left him in dreamland. Only Bukayo Saka has contributed more goals and assists (72 to 51) for Arsenal since the Belgian made his debut for the club in January 2023. The forward assisted Martin Zubimendi just seconds after coming on against Nottingham Forest, and once again showed why he is such an important player in this squad for Arteta in Spain.

Squad depth has been a theme of Arsenal's last week. It has been demonstrated in the Premier League. Now it has, too, in Europe.

It was clear within minutes of kick-off that Arsenal were not going to have the freedom afforded them when they thrashed Athletic 3-0 just last month in a pre-season friendly.

The hosts started the game with real urgency and aggression, meaning Arsenal had to battle for a foothold. And it was Gyokeres who stepped up in this regard around the midway point of the first half.

Initially, it was two runs in behind the Athletic defence that helped give Arsenal a platform in the opposition half. His first run ended in a slightly tame effort at goal, Unai Simon gathering with ease, but his second gained his team-mates their first real feel for the ball in dangerous areas.

The Sweden international was unlucky that he could not guide Jurrien Timber's cross into the net, but he was giving his team-mates a target to hit, and an out ball to puncture the Athletic pressure.

His inadvertent head clash with Gabriel left a nasty gash but, while it left him bloodied, was not too serious. Once patched up and out for the second half, he should have at least guided his first header on target from Rice's wide free kick.

Yet Gyokeres did well to combine with Noni Madueke more in the second half as the winger continued his rich vein of form, with more direct running and smart combination play.

The change to bring on Leandro Trossard for Gyokeres was slightly different to the switch instigated by Arteta against Nottingham Forest when bringing the striker off. This time Trossard went up front and Mikel Merino stayed in midfield, nominally as a No 10 -- a move which almost paid off immediately as the Spaniard headed an Eze cross towards goal. Again, Simon conjured the save.

With Martin Odegaard ruled out with a shoulder injury, some may have liked to have seen Rice wear the captain's armband in Bilbao, but it was Gabriel who ultimately showed why he was entrusted with that responsibility.

The Brazil international has been a key figure for Arteta's Arsenal since signing in 2020, and played an important role in ensuring they weren't overawed by the atmosphere.

With the game stretched at times, the 27-year-old was always ready to engage on the front foot when necessary but also displayed patience in key moments at 0-0. That, as well as his management of the tenser moments of a tight contest, kept his side level-headed in the cauldron of the Estadio de San Mames.

A real force at the back, there was no chance that Arsenal would be intimidated or bullied by the home side's onslaught. Alongside Gabriel, Cristhian Mosquera was just as impressive with his recovery pace and stature key to keeping Arsenal level before Martinelli's thrust them ahead.

This was not the first time Gabriel had skippered the side, and it definitely won't be the last. When asked about who has taken Jorginho's place in the club's leadership group last month, Arteta said: "I think at some point it will come out. There are a few players, a few names. Very happy with the outcome. The way it was done as well.

Athletic Club 0 Arsenal 2: Martinelli and the super-subs - and is Gabriel justifying the armband?