Champions League: What Arsenal, Barcelona and Inter must change to advance to the final in Munich

Week one of the Champions League semifinals is done and dusted, and, well, that was something special. Tuesday delivered a slow-burning thriller even if Paris Saint-Germain flew out of the traps at the Emirates Stadium, taking an early lead that they would hold onto quite impressively without ever quite giving the impression they'd brushed Arsenal out of the tie.

If that was a more cerebral encounter, Barcelona's 3-3 draw with Inter asked nothing of its viewers beyond drinking it all in. A deft Marcus Thuram flick, the fastest goal ever scored in a Champions League semifinal, would have lit up any game, but it barely registered as a footnote on the night of Denzel Dumfries' double, Lamine Yamal's brilliance, and a thunderbolt from Raphinha (that was ruled an own goal)

That draw means both sides will meet at the San Siro next Tuesday, convinced there is a lot more work yet to be done. While Luis Enrique insisted after his side's win that their lead was a tenuous one, there is plenty for Arsenal to do too. What do they and the two sides from Wednesday's draw need to address over the coming days? Let's find out:

1. Barcelona: Tidy up set pieces

After such a brilliant performance, there are precious few big issues for Barcelona to address (you could say much the same about Inter). They are not going to stop taking those risks with their kamikaze high defensive line, a week out from their biggest away game of the season so far, and on the evidence present at Montjuic, you can see why. When eight or nine players are within 20 yards of the ball, it really is quite easy to dictate the terms of engagement, to swarm in the counter press, to bounce wall passes off. Whatever happens, Barcelona are going to have the best attacker on the pitch. The only question is going to be whether it's Raphinha or Lamine Yamal. Maybe even a revived Robert Lewandowski?

A wrinkle to address, however, is a set-piece defense that gave up two broadly preventable goals to Denzel Dumfries. Set pieces had not been a particular problem for Barcelona before this semifinal, at most bubbling under the surface during the knockout stages as first Nicolas Otamendi and then Serhou Guirassy undid them from corners. Now it has burst through. No wonder. Barcelona hadn't run into a team quite as big and muscular as Inter before now.

There was no great trickery to what Inter did on their corners, just getting the ball in the mixer and winning their headers. A relatively simple bit of blocking by Acerbi freed Dumfries for his second, a poacher's finish got the right back the first. It will always be harder for Barcelona, who are giving up a lot in terms of size to their opponents from Serie A, but there might be some quick and effective adjustments that can be made.

Most of all, Wojciech Szczesny, all 6-foot-5 of him, is going to have to come for the ball whenever it is swinging inwards. Whatever he does from any set piece, it has to be done more convincingly than for the second Dumfries goal. Too often, the Polish veteran seems to find himself in the nethersphere between ball and his own line, not just from set pieces but from the Henrikh Mkhitaryan goal that wasn't quite onside. That second corner was too deep, too far back. Had Szczesny stayed on his line, it would surely have looped into his hands.

Sorting their dead ball defense won't entirely quell Inter, but there are some risks that you price in to play the game you want to. The way they defended corners needn't have been one of those gambles.

2. Inter: Wear smaller boots

Credit to Simone Inzaghi, you could not have accused him of playing for the draw he got in Barcelona. So much of their defensive setup seemed framed around where Inter players would be if and when they got the turnover. If that meant leaving Alessandro Bastoni one-on-one with Yamal, maybe that was a risk worth taking to get Federico Dimarco in prime positions. How close was it to paying off in spectacular fashion? About the length of Mkhitaryan's big toe.

This was one of five occasions Barcelona could say they had caught the Inter attack offside. For most teams, that would be remarkable execution of a high wire. For Barcelona, that's Wednesday. So far this season, there have been 12 games in Europe's top five leagues and continental competitions where a team has been caught offside on nine or more occasions. Eight of those have been against Barcelona. It really works.

Even having said that, Inter's best bet might still be to find the moments that it doesn't. There is space there, and with or without Lautaro Martinez, they have enough players to exploit it. All you need to do is squeeze them into the smallest boots they'll fit into.

3. Arsenal: Get it launched

We know something changed after the bruising quarter-hour beatdown that Khvicha Kvaratskhelia and company inflicted on the Emirates Stadium on Tuesday night. Mikel Arteta said as much, and it was easy to see why. When asked what had changed, he refused to make much of a comment beyond that he had addressed something "very specific, but very important." Whatever had changed worked. From then until at least the 70th minute, when tired legs started to show among the home team, Arsenal were at least PSG's equal.

There were a couple of adjustments that were apparent after Arsenal's slow start. After purposefully joining Leandro Trossard in the first line of a 4-4-2 press early on, Martin Odegaard eased up, at least for a while, meaning the hosts more often defended in a 4-2-3-1 that was about blocking passing lanes more than it was winning a duel. At the very least, it slowed PSG, Mikel Merino even managed one very dangerous regain high up the pitch.

In possession, meanwhile, Arsenal adapted. They had done what they could early on to play their way through the PSG press and no wonder, this is a team that are usually as at ease in a vice grip as Harry Houdini. They will probably be more effective at doing so in the Parc des Princes now that Thomas Partey has served the suspension for his ludicrously foolish yellow card late on against Real Madrid.

Partey's return should also allow Declan Rice and Merino to move up a line, in the process giving Arsenal more height at the top of the pitch. That is what they exploited most effectively as the game wore on. In those first 15 minutes, 40 percent of the Gunners' passes went long, a fair proportion lower than the 46.6 percent they average in the Premier League this season. For the remainder of the game, over 60 percent of Arsenal's passes went long.

Against these particular opponents, it worked. The raking passes out wide to Bukayo Saka pulled Kvaratskhelia back and the England international had the strength to get away from Nuno Mendes. On the opposite flank Gabriel Martinelli often found himself running at relatively open field, Achraf Hakimi having pushed upfield. Arsenal never quite made as much as they might have from Marquinhos being dragged wide. Through the middle too, those searching balls to Merino, not least the Martin Odegaard free kick that found him marginally offside. Get Rice up higher too and Arsenal can be confident that if the ball goes deep and high, they'll get the first and/or the second ball.

For once it feels like Arsenal have run into a team that are quicker and technically better than they are. What PSG aren't, however, is taller and stronger. If the Gunners are going to do something remarkable in the Parc des Princes they're going to have to exploit that reality, one even a coaching mind as excellent as Luis Enrique can't change.