Mariona Caldentey's second-half stoppage-time penalty secured Arsenal a dramatic 1-0 win over Danish side HB Koge to open their Champions League campaign at Meadow Park.
There were wholesale changes for Gunners boss Renee Slegers, who inserted eight different faces into her starting line-up from Sunday's 1-1 Women's Super League draw with Manchester United.
Chloe Kelly had the ball in the back of the net in the first half, but the England forward's would-be opener was disallowed following a VAR check.
Arsenal, who had lacked end product throughout, were gifted an opportunity when Selina Cerci was brought down and substitute Caldentey secured all three points with a bottom-corner finish.
Greek referee Eleni Antoniu was called to the monitor after Kelly beat Alberte Vingum in the 12th minute, but it was chalked off after it was determined Stina Blackstenius had been offside in the build-up.
Maanum drew another save in the 25th minute, with the game rarely venturing outside the visitors' half until Macy Schultz's deflected effort drifted towards the crossbar.
There was a cross-shot from Maanum, who could not connect with a team-mate, before a Kyra Cooney-Cross effort also drifted wide.
Blackstenius was replaced by Alessia Russo after the break and there were a couple of Arsenal chances in quick succession in what started as a more end-to-end opening to the second half, including a Smilla Holmberg free-kick punched away by Vingum.
The clinical finish, though, still evaded Arsenal, who wasted a handful of set-pieces and watched as Maanum directed an effort over the bar.
Holmberg prevented danger with an alert clearance after Emelia Oskarsdottir's cross fell loose, then came within a couple of inches as her corner caught the crossbar directly.
Then, in the third of four minutes of stoppage time, Yukina Sakabe sent Cerci tumbling. Antoniou pointed to the spot, and Caldentey buried the ball past Vingum.
Arsenal Women boss Renee Slegers told the club's official website:
"[I'm pleased with] the three points and the mentality, resilience that we've been building to get late goals that are important for us. Again, a lot of dominance, but we don't get the goal.
"But like I said, the mentality and that's something we're going to bring into the season, that we can do things this way as well. And then we continue to work on football.
"I think there's all new teams starting today compared to last weekend. We have five players coming in, making their impact. I think Selina [Cerci] creates the penalty. Mariona [Caldentey] scores the penalty, two players coming on. And that's what we're about.
"That's how we want to do things together as a squad and everyone having their impact. So from that perspective, I'm really happy and really proud."
Manchester City's eventful return to the Women's Champions League saw them come from 2-0 down to draw 2-2 away to Bayern Munich and become the first English side to avoid defeat to the Germans in Europe.
City's Germany international Carlotta Wamser was left completely unmarked in the penalty area to score her first City goal in the 86th minute after prolific striker Khadija "Bunny" Shaw had earlier missed a penalty to equalise.
The visitors were worthy of a point based on their second-half performance, having been completely dominated before the interval before nicking a goal on the stroke of half-time.
Bayern were 2-0 up inside the first half-hour and had chances to put the result beyond doubt, but with seconds ticking down to the interval Kerstin Casparij's break down the right led to Beth Mead eventually tapping in.
However, the hosts were unhappy that play had been allowed to continue, with a flare thrown onto the pitch as the attack developed. Casparij had crossed the ball before reaching the thick blue cloud, though, and the goal was allowed to stand.
It was the stroke of luck City needed, and they benefited again when Ena Mahmutovic appeared caught between two minds as she raced out to close down Aoba Fujino.
The goalkeeper initially appeared content to let the ball run out of play, only to inexplicably stick out a leg and bring down the City winger.
Shaw, who had been due to be substituted, could not capitalise and was immediately replaced. Wamser, however, ensured the miss did not prove costly.
City were fortunate to have only a two-goal deficit to overturn, with Klara Buhl and Pernille Harder both going close before Giulia Gwinn's chipped effort across Ayaka Yamashita opened the scoring in the 11th minute.
Linda Dallmann had been allowed to drive unchallenged from the halfway line before finding Gwinn, who calmly lifted the ball over Yamashita and into the far corner.
Buhl then volleyed straight at Yamashita, while Jovana Damjanović blazed over as Bayern cut through City's midfield once again.
Lauren Hemp almost conjured a goal out of nothing when her deflected cross clipped the top of the crossbar, but it proved only a brief respite.
Harder soon whipped a cross into the box, with Casparij making a complete mess of her attempted clearance and inadvertently diverting the ball into her own net.
Man City Women midfielder Sam Coffey told the club's official website:
"Beth's goal changed momentum going into half-time. We connected better and were more front-footed in the second half. So it was huge to take that into half-time and continue to turn the game around.
"We wanted to win the game, so we're disappointed we didn't do that, but to come away from a really tough place with a draw is something we should be proud of."
On the subs: "It's one of the best parts of our team of how deep we are. We have so many gamechangers and whoever comes into the game is going to have an impact on it.
"That's what the best teams in the world need and want, and I think we have that to the nth degree."
