Massimiliano Allegri was critical of Juventus' second-half performance after they reached the Europa League quarter-finals with a 2-0 win at Freiburg on Thursday.

Juve built on their 1-0 first-leg advantage as Dusan Vlahovic converted a first-half penalty after home defender Manuel Gulde was controversially sent off for handball inside his own area.

Federico Chiesa added a late second after entering the fray as a substitute, as Juventus maintained their bid for a first major continental title since they won the Champions League in 1996.

However, Allegri was displeased with Juventus' performance after Freiburg went down to 10 men, saying the Bianconeri must improve if they are to progress further in the competition.

"The team got a good result as we progressed. We made a lot of mistakes in the second half with our ball handling, and we need to improve," he said at his post-match press conference.

"We can't play a second half like this against a team of 10. We were made to defend our own box. The second half should have been better. We need to work; we made a lot of wrong decisions.

"Against 10 we lowered our attention and pace. The result is good – excellent even – but let's not get excited because we're in the quarter-finals. We have to think about what we did in the second half and improve."

Chiesa's stoppage-time goal – a driven strike which found the net via the foot of the post – was just his second since returning from an anterior cruciate ligament injury in November, and the Italy international is looking to find consistency in the coming weeks.

"My first thought is to be available to the coach. Unfortunately I haven't been there in the last few games," he said. "There's still a bit of discomfort, but I'm working even harder to be more ready.

"Unfortunately my father [former Italy striker Enrico Chiesa] had similar injuries. It's a path of great obstacles to come back, but even after that, the journey continues. I just have to stay calm."

Meanwhile, the decision to send Gulde off after his outstretched arm was struck by Federico Gatti's shot infuriated Freiburg boss Christian Streich, as did a failure to punish Wojciech Szczesny for seemingly picking up a Manuel Locatelli back-pass.

"We were brave, we went for it," the Freiburg boss said. "Then there was the situation with the red card and the penalty. That was of course a difficult situation for us.

"I'm speechless. In both games, after every foul, a Juve player plays the ball away. Always. It's a complete mystery to me.

"Then there's the intentional back-pass that isn't blown. It's difficult to accept. Something that was crucial was let go."