Arsenal made hard work of the triumph, but they wrapped up three critical points away at Benfica.
The Champions League holders were eager to put points on the board for the first time this campaign and dominated most of the ball in Lisbon, but they could not break the deadlock before half-time.
The struggle continued in the second half, but Beth Mead calmed down the nerves with a strike on the verge of the hour mark. The contest remained in the balance until the 89th minute when Alessia Russo doubled the advantage, ensuring that Lisbon remained a happy hunting ground for the Gunners.
Both clubs came into this clash trying to make up for defeats in their first European fixture. Benfica took an early advantage in Italy on opening matchday, but they lost 2-1 to Juventus. Meanwhile, Arsenal sacrificed a lead inside fifteen minutes against OL Lyonnes, also ending up pointless.
Benfica head coach Ivan Baptista rotated three members of the starting eleven he used at Juventus. Carole Costa came out of central defence, and Christy Ucheibe stepped in next to Diana Gomes. Carolina Tristao, who does not turn 17 until next month, also started in the middle of the park.
The last alteration was enforced. Nycole Raysla was stretchered off in a fixture on the weekend, so Caroline Moller moved up front, and Diana Silva shuffled into the attacking unit with Lucia Alves.
The big change from Renee Slegers involved the midfield unit. Frida Maanum made way for Kyra Cooney-Cross, who impressed in the second half against the Seagulls. Kim Little joined her in the double pivot, and Mariona Caldentey acted as the most offensive midfielder from the trio.
Beth Mead replaced Caitlin Foord, Olivia Smith stayed on the right wing after her game-winning intervention on the weekend, and Alessia Russo remained as the central forward. Lotte Wubben-Mooy came in for Katie Reid, and Taylor Hinds started as the left back ahead of Taylor Hinds.
The last time Arsenal had been to Lisbon was for the Champions League final and a hard-fought win against Barcelona. Though still to be respected, Benfica were not the same level of opposition, and Arsenal could apply a much more aggressive approach to trying to take a positive result.
The hosts only kept 31% of the ball in the first twenty minutes of the match, and their one notable opening, engineered through a brilliant pass from Moller, still left Silva at an acute angle to shoot.
However, the feeling was that the guests were not sharp enough to make the most of their openings.
A couple of moments near the half-hour mark proved the point. Firstly, Russo received a Mariona flick-in smartly, swivelled and set away Mead, who was too slow to get off a strike. She did win a corner and Wubben-Mooy lurked at the far post for the delivery, but a free header drifted wide.
Moments later, Mead again profited from sharp work without the ball to intercept a switch. She broke forward into the final third, cut back on herself, but failed to hit a clean shot or connect with Mariona. Chances were passing by the Gunners, and at this level, there is the quality to punish wastefulness.
The visitors nearly suffered a killer blow in the 41st minute. Anna Gasper swung a free kick into the Arsenal penalty area, and Catarina Amado forced Daphne van Domselaar to dive and deny her.
The Gunners continued to knock, and eventually, they got the luck that they were looking for.
On the verge of half-time, Silva swung wildly at the ball and gave away a corner that was not fully exploited. But by the 57th minute, the hosts had made one mistake too many against the title holders.
Cooney-Cross picked up the pieces from some loose passing in the buildup, and Russo slipped the ball down the line for Mariona to run into the danger zone. Her cutback was a few inches short of reaching Mead, but the ball ricocheted off two defenders and fell to the forward, who snatched the opportunity.
Slegers soon called on the cavalry, sending on Stina Blackstenius and Chloe Kelly in the attack. The Swedish striker nearly had a free run at goal from a miscued header, and Kelly tried to catch the goalkeeper off her line, looking for a second strike to kill a contest that was still largely in favour of the Gunners.
Benfica had not given up the fight, but they rarely came close to scoring themselves either. It would come down to Slegers’ side to seal the deal in the closing moments of the allotted ninety minutes.
Foord, who had swapped in for Smith, blocked a defender as Kelly fed a free kick along the floor. Russo ran freely into the box, and she struck decisively to secure the three points for the visitors.
Ucheibe came close to forcing a significant error out of van Domselaar as Gasper delivered another pinpoint cross from a set-piece in injury time, but the clean sheet would also remain intact in Lisbon.
Player of the Match: Kyra Cooney-Cross
Cooney-Cross built on the cameo she put on against Brighton with a solid showing from the start.
This fixture was not the best showcase of the fluidity and flowing moves that Arsenal can string together, but they did demonstrate that they have the grit to grind out a result if necessary. With the energy and endeavour that the midfielder brought to the table, the visitors were able to compete.
She might have got an assist with her cross for Wubben-Mooy before the break and neatly set off the transition that produced the game opener from Mead. The international break is looming, but Cooney-Cross will hope that there is more to come in terms of playing time and strong form in November.