Madrid - When Fernando Torres left Atletico Madrid for Liverpool in 2007, the idea of the Spanish capital's second club being favourites to beat record winners Barcelona in a two-legged King's Cup tie would have been unthinkable.
Now that the 30-year-old Spain forward is back in his boyhood team on loan, he has seen at first hand how coach Diego Simeone has shaken up the status quo and transformed Atletico into genuine contenders at home and in Europe.
While Barca may still be expected to edge the Cup quarter-final ahead of Wednesday's first leg at the Nou Camp, the way Atletico have been playing under the inspirational Argentine the past couple of seasons means they have every chance of progressing to the last four.
Torres struck twice in last week's 2-2 draw in their last 16, second leg at Real Madrid as Simeone's men dumped the holders out 4-2 on aggregate.
The return of "El Nino" (The Kid) has lifted the Atletico players, as well as long-suffering fans already on a high after the club won La Liga last season for the first time in 18 years and lost out to Real in the Champions League final.
"The arrival of Fernando is very good for us," midfielder Raul Garcia told Spanish television after Sunday's 2-0 La Liga win at home to Granada.
"He gives the team extra options," added the Spain international. "Good players always understand each other."
Barca, who thrashed Elche 9-0 on aggregate in the last 16, also warmed up for Wednesday's clash with a win in La Liga, Lionel Messi netting his 22nd hat-trick in Spain's top flight in a 4-0 success at Deportivo La Coruna.
Victory in Galicia came a week after Barca beat Atletico 3-1 at the Nou Camp in La Liga but Spain playmaker Andres Iniesta warned against taking another win for granted.
Villarreal or Getafe await in the last four, while on the other side of the draw Sevilla play Espanyol and Malaga meet Athletic Bilbao, whose 23 Cup triumphs are bettered only by Barca's 26.
"These will be a fun couple of weeks but it will be a very intense tie and Atletico are tough opponents," Iniesta told reporters.
"We will have to do things as well as possible without making any mistakes," he added.
Barca last won the Cup in 2012 and Atletico beat Real to secure their 10th triumph in 2013.