Now both are within reach, starting with the second leg of their European semi-final at home to Atletico Madrid on Tuesday (Wednesday AEST).
The first leg ended 1-1 in Madrid last week after a pair of penalty goals for two teams looking for a first European Cup title.
Arsenal will be hoping its home field advantage at Emirates Stadium makes the difference in the return.
"After 20 years to be in this position again," Arsenal manager Mikel Arteta said, "we are so hungry to get the game that we want and go through to that final."
Arsenal routed Atletico 4-0 at home in the league phase in October, but expect Diego Simeone's side to be a lot more solid defensively in the return to London.
"I'm going to try to tell the team to play like they did in the second half (in Madrid)," Simeone said. "If it's that easy it would be great. We have a lot of faith in what we're doing."
Both teams have been boosted by injury returns. Forward Julian Alvarez is expected to play for Atletico, while Arteta said captain Martin Odegaard and forward Kai Havertz were both available.
Atletico have reached the final twice under Simeone, in 2014 and 2016, losing both times to crosstown rival Real Madrid. Arsenal lost its only final in 2006 to Barcelona.
This time, defending champion Paris Saint-Germain or Bayern Munich will await the winner. Those two play their second leg on Wednesday after a pulsating 5-4 win for PSG in the first leg.
Arsenal's quest for a first Premier League title was also boosted on Monday by Manchester City drawing at Everton 3-3, meaning the Gunners can clinch the trophy by winning their last three games.
Atletico is only fourth in La Liga, 25 points behind leader Barcelona.
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