The Spanish side did not look like they were a team currently seventh in the standings in the La Liga.
They took on Manchester United, much to the surprise of many watching the game, and repeatedly unlocked the Mancunian defence that has conceded less than a goal per game after 28 matches in the Premier League.
Coach Marcelo Bielsa has earned plaudits for his tactical awareness as he played a high-pressing game and exploited weaknesses in United's strategy. Not only were they able to score three goals at Old Trafford last week, the Argentinean masterminded a 2-1 victory in Bilbao on Thursday night with Wayne Rooney's goal for United coming late in the game when the result was a foregone conclusion.
The Red Devils' custodian David De Gea congratulated his opponents calling them a "superior side" and wishing that Athletic "go all the way to the final".
Toquero was in an equally bullish mood and believes that Bilbao have what it takes to beat anyone in the competition after conquering the current Premier League leaders.
He told UEFA.com: "Manchester United will always be Manchester United but this time we deserved our result and we deserved to get through.
"Let's see who we get in the draw but whoever it may be the important thing is that we continue along the path we are on now.
"We don't care who we get because we know we are capable of beating anyone.
"We've shown that tonight [Thursday]."
He also said that his team performed so well because they had taken nothing for granted before the game.
"We went out there tonight to have possession of the ball and to win.
"We didn't want to mull over the result of the first leg so we decided to go for it and it paid off thanks to a lot of hard work, dedication and a little luck.
"We created a lot of chances in order to win.
"We did our job well."
Goalkeeper Gorka Iraizoz thanked the passionate support of the fans who he believed were crucial in inspiring the team to win against United.
"We played two fantastic legs and we were switched on from the outset of both games, as were our fans," he said.
"For our people, for our fans, this tournament is so important."
"We are so lucky to be able to plant hope within our supporters; that's like a gift to us.
"I hope in future I will get to compete in another tie like that."