Milan head coach Stefano Pioli was left frustrated that key decisions went against his side in their 2-1 Champions League defeat to Atletico Madrid.

The Rossoneri were deservedly ahead through Rafael Leao after 20 minutes at San Siro before Franck Kessie received a second yellow card for catching Marcos Llorente on the foot.

The home side survived until the 84th minute when substitute Antoine Griezmann swept home a fine first-time finish to level the scores on Tuesday.

Then, deep into injury time, referee Cuneyt Cakir awarded a penalty against Pierre Kalulu for handball, allowing Luis Suarez to net the 97th-minute winner.

"More than anger, there's disappointment. We were close to an important result," Pioli told Sky Sport Italia.

"At 11 versus 11, we played much better. It's a shame because a little more attention was needed for the first goal. The boys made an important effort and losing complicates qualification for us.

"We're still missing that piece that can make the difference. We're not missing much. We played great football for half an hour, [and] we suffered when outnumbered. It's a performance that must give us confidence."

He added on the Kessie red card: "Franck had already been booked. It didn't look like a second-yellow offence in the 30th minute of the first half. The referee was certainly not the best on the pitch tonight."

The result put Atleti two points behind group leaders Liverpool and four clear of Milan, who lost to Jurgen Klopp's side on matchday one.

Diego Simeone admitted Atletico had been second best until Kessie's dismissal changed the course of the contest.

"In the first 30 minutes, they put us under pressure and we didn't have the tools to get out," he told reporters.

"Then, they were left with a man down and the game changed from there. We managed to impose ourselves in the second half.

"We have great room for improvement. We need to find that consistency in creating play and doing the right actions."