Pioli concedes the result was a setback.
“I totally agree [we did too little]," Pioli told MilanTV. “Even if we could have won it with Kessie at the end.
“We did too little, we played without rhythm and our approach was not the right one. It was a complicated match for us."
Fabio Quagliarella struck for Samp, with Jens Petter Hauge scoring for the Rossoneri.
“Sampdoria played in the same way they played in the first leg," Pioli said. “Today, there was less rhythm, we favoured their defence, which was well organised. I find it hard to be happy.
“The performance had to be different, there were all the right situations to play with more intensity and quality.
“This must make us disappointed and embittered, now we must show that we can start again immediately."