And debutant Murillo is hoping Barca, without Lionel Messi and Luis Suarez on the night, can build on Coutinho's strike in the second leg.
The defending champions were heading for a convincing defeat following early goals from Erick Cabaco and Borja Mayoral, who is on loan from Barca's rivals Real Madrid.
The home side struck twice within the opening 20 minutes to take control of the contest.
Sevilla will take a commanding lead into the second leg on home soil after they defeated Athletic Bilbao 3-1 at San Mames.
"The game also served to check out some players in a La Liga-level game".
Valverde added that he was "happy" with centre-back Murillo's first showing since signing on a six-month loan from Valencia but conceded it had been a "difficult test" for Miranda and Chumi, who were both substituted.
The Brazilian star joined the club last January in a deal worth an estimated 160 million euros but the recent form of the former Liverpool man has become noticeable of late.
Barcelona assistant manager Jon Aspiazu spoke of Philippe Coutinho's current form, suggesting that Ousmane Dembele is now outperforming his teammate. I will say the same about Dembele. What the players have to do is work hard to revert the situation. And if one of them isn't happy, they have to fight to turn things around.
Valverde introduced Arsenal-linked Denis Suarez off the bench and it was the midfielder's mazy dribble that invited Coke into a clumsy challenge, allowing Coutinho to give Barca a much-needed foothold ahead of the return encounter.
He said: "Everyone wants to play". There's tough competition here [for places]. There are a lot of midfielders and only three positions.
"This is a period of the season when fixtures come thick and fast and we will need to make rotations, I am aware of this and so are the players".