La Liga high-flyers Atletico Madrid came from behind to beat Reus Deportiu 2-1 in the first leg of their fourth-round Copa del Rey tie at the Estadio Camp Nou Municipal on Tuesday.
Atletico - 10-time winners of the competition - made a number of changes from their weekend victory over Espanyol and were pushed hard by their third-tier hosts, who acquitted themselves well.
Deportiu, leaders of the Segunda B's Group 3, made the most of some sloppy Atleti defending half an hour in as Fran Carbia tucked home the opener.
However, Diego Simeone's men ensured they stretched their unbeaten run to 11 games in all competitions courtesy of headers either side of half-time.
Luciano Vietto levelled before the break while Saul Niguez scored the winner just after the hour to earn Atleti an advantage ahead of the second leg at the Vicente Calderon in 16 days' time.
Simeone named an entirely different defence from Saturday's league win and brought midfielder Thomas Partey in for Tiago, who suffered a broken leg at the weekend.
And Simeone's men should have led six minutes in when Vietto was thwarted by Edgar Badia inside the area, having been played in by some intricate passing play.
Miguel Angel Moya, making his first Atleti appearance of the season, was required to deal with a looping cross that veered goal-wards before Badia was called on to deny Angel Correa at the other end.
However, Deportiu took the lead with their first shot on target half an hour in, as Fran pounced on a mistake by Lucas Hernandez before prodding the ball past Moya.
The lead proved short-lived as Atleti drew level nine minutes before the break when Vietto connected with Oliver Torres' cross to beat Badia with a header low to his left.
Captain Koke tested Badia early in the second half but the hosts continued to make life difficult for Atleti, limiting space and causing problems on the break.
Correa skewed a shot wide on the hour before Atleti's pressure eventually told, Saul connecting with Koke's corner to beat Badia with a looping header the home goalkeeper was unable to keep out.
Deportiu had negotiated ties with Asco, Arandina and Lleida Esportiu to reach the fourth round, while avoiding defeat in all competitions since their loss to Sabadell in mid-October.
Despite a spirited effort to find an equaliser late on - Ricardo Vaz glancing a header over the crossbar - the visitors held firm to begin a sequence of six games in 20 days with a hard-fought win, taking a narrow advantage back to the capital.