Gelson Martins marked his full debut for Atletico Madrid with the only goal of the game as they claimed a 1-0 victory over Sant Andreu in the Copa del Rey.
The Portugal international had managed only 57 minutes of football for Atletico this season before Tuesday's last-32 first leg, but provided the telling moment of quality in Barcelona, while the likes of Antoine Griezmann, Diego Costa, Diego Godin and Koke were all rested.
Sant Andreu, who play in Spain's fourth tier, provided a solid test for Diego Simeone's side and should have snatched an equaliser through centre-back Joan Noguera late on.
Atletico themselves squandered a handful of chances to make the win safe, but they will certainly be expected to complete the job at the Wanda Metropolitano on December 5.
Gelson had tested goalkeeper Jose Segovia in a surprisingly even first half-hour, and it was the winger who gave Atletico the lead 33 minutes in, slotting home after just beating the offside trap to reach Vitolo's prodded pass.
Atletico suddenly looked in control and should have been given the chance to make it 2-0 from the penalty spot, but referee Jesus Gil Manzano was unmoved after Santiago Arias was scythed down in the box.
A rather pedestrian second half was dictated by Atletico, but they failed to make the most of their opportunities, with Nikola Kalinic seeing a shot blocked and Arias dragging an effort narrowly wide of the left-hand post.
Antonio Adan was forced to claw away a bouncing effort from Elhadji Bandeh in the closing stages, but it was Noguera who wasted Sant Andreu's best chance, heading the ball off the turf and against the crossbar with the goal gaping after he found space from a corner.
93' | 0-1 | ¡Final! ¡Termina el partido en el Narcís Sala!¡Victoria del equipo gracias al tanto de ! ¡La eliminatoria se decidirá en el Wanda ! October 30, 2018
What does it mean? Atletico in charge and Gelson up and running
Having struggled for game time since moving to the club from Sporting CP, Gelson's outing in Barcelona will do a huge amount for his confidence and fitness, even if it was against modest opposition.
In terms of the tie, Atletico are certainly in control of matters and it would take a monumental shock for them not to reach the last 16 of the competition following the second leg.
For now, Simeone will be happy the players involved came through unscathed ahead of a gruelling run of matches in November, which includes two Champions League matches and a league fixture against Barcelona.
Signs are good for Gelson
Atletico's strength in depth in attack would make it tough for most forwards to play regularly, but Gelson might have done enough here to earn more frequent playing time in LaLiga and the Champions League.
He took his goal well and certainly looked sharp when drifting wide and cutting back in towards the box. With Atletico facing a serious fixture pile-up in the coming weeks, he could be a real asset.
1 - Gelson Martins has scored his first goal for in his first start for the club in all competitions (four apperances). Confidence. October 30, 2018
Lemar not yet on song
Thomas Lemar has not quite hit the ground running since his move to Spain, and this was another damp squib of a performance in the rain.
The France winger was far from abysmal, but Simeone would be entitled to expect more from the hour Lemar had on the pitch.
What's next?
There is over a month until Sant Andreu visit the capital for the return leg, and Atletico have a fearsome schedule in the intervening weeks, with games against Leganes, Borussia Dortmund, Athletic Bilbao, Barcelona and Monaco all to come in November.
