Mikel Arteta handed Reiss Nelson a start on the left of the attack after his show stopping strike salvaged Arsenal a dramatic comeback victory over Bournemouth last weekend to keep them top of the Premier League.
The Arsenal coach also gave Polish defender Jakub Kiwior his debut after his January arrival from Spezia.
It was his centre-back partner William Saliba who headed home from Fabio Vieira’s corner to put Arsenal ahead after 22 minutes at the Jose Alvalade Stadium in Lisbon.
Former Liverpool defender Sebastian Coates was booked during an argument in the aftermath of the goal, meaning he is suspended for the second leg next week.
Sporting equalised shortly after in near identical fashion, with Inacio heading home Marcus Edwards’ corner.
Former Tottenham midfielder Edwards then forced a fine save from Arsenal goalkeeper Matt Turner, as the hosts stepped up a gear.
Sporting goalkeeper Antonio Adan did well to deny Gabriel Martinelli early in the second half, and his team capitalised to take the lead.
Edwards’ clever reverse pass split open Arsenal’s defence and after Pedro Goncalves’ shot was deflected, Paulinho reacted quickest to finish.
Martinelli nearly equalised with a brilliant run from halfway but, after rounding Adan, was foiled by a last-gasp Jeremiah St. Juste slide tackle.
Arsenal were level just after the hour mark, though, when Granit Xhaka tried to find Martinelli but Morita deflected the ball into his own net to leave the game on a knife-edge in the second leg.
– Roma comfortable –
Mourinho’s Roma were good value for their victory against Real Sociedad with Stephan El Shaarawy sending the hosts ahead in the Italian capital from close range after a fine run and cross by Tammy Abraham.
Take Kubo struck the post at the other end as the Basques battled back in search of an equaliser.
Roma struck again towards the end as Albanian defender Marash Kumbulla powered home a header from Paulo Dybala’s in swinging corner, giving them a strong advantage to take to San Sebastian.
Bundesliga surprise package Union Berlin snatched a 3-3 draw against Belgian side Royale Union SG, while Bayer Leverkusen beat Ferencvaros 2-0 at home.
In the UEFA Conference League, Michael Antonio hit two first half goals to earn West Ham a 2-0 win at EK Larnaca, while Villarreal shared a 1-1 draw with Anderlect.
Manu Trigueros put the Spanish visitors in front but Anders Dreyer levelled early in the second half.