The Italian concedes his side showed "too much respect" towards Jose Mourinho's men and feels his side could have scored a second goal in Wednesday's 1-1 draw
Early pressure from Jose Mourinho's side was rewarded with a ninth-minute opener from Fernando Torres at the Turk Telekom Arena, but the hosts battled back after the break to earn a draw through Aurelien Chedjou's equaliser.
The scoreline means the tie is still finely balanced heading into the return leg at Stamford Bridge on March 18, with an away goal giving the Premier League side a slight edge, but Mancini feels his side could have been heading to London in a more comfortable position.
Asked by Sky Sports whether he was disappointed to be coming away on level terms, the Italian said: "Yes, because in the second half we probably deserved to score another goal.
"We gained a lot of confidence from the second half, but we had too much respect for Chelsea. Maybe we were too deep in the first half, we played with fear but I'm happy.
"One-one is a good result, we have another game."