Diego Simeone admitted Atlético Madrid were "hurt" by a 2-1 defeat at Espanyol in their opening LaLiga game of the season, after the team failed to capitalize on Julián Álvarez's sensational first-half free kick.
Atlético were on top at the RCDE Stadium when Álvarez put the visitors ahead in the 37th minute, but late goals from Miguel Rubio and Pere Milla gave Espanyol -- cheered on by new shareholder and former NFL defensive end J.J. Watt -- all three points on Sunday.
Simeone gave debuts to five of Atlético's summer signings in the starting 11, including USMNT midfielder Johnny Cardoso, who was substituted at halftime.
"They [Espanyol] made the most of the situations they had," Simeone told Movistar in a post-match interview. "The set piece [for Rubio's goal] got them into the game. We had the game well controlled. And then with the second goal, that hurt us."
Atlético have invested heavily this summer, bringing in seven new players, as they look to compete with Barcelona and Real Madrid after ending last season without a trophy.
"It's part of the journey," Simeone said. "This result hurts us, but it can also make us improve and grow. I'll focus on the good things the team did, and we'll try to reduce the deficiencies that we saw.
"The team played well. They [Espanyol] didn't have chances. We had control of the game, we were moving the ball well... but the most important thing is winning."
Club captain Koke was introduced at halftime alongside Pablo Barrios, as Cardoso and midfield partner Conor Gallagher were replaced by Simeone.
"Football is about being clinical in both boxes, and we weren't," Koke said. "We know what this level demands.
"We'll have to be clinical if we want to do something in this league."
NFL legend Watt is involved with Velocity Sports Limited, the owners of Premier League club Burnley, who took over Espanyol this summer.
The three-time NFL Defensive Player of the Year posted a video on social media, mingling with Espanyol fans before the game.