Samp played with 10 men for the entire second half following Enzo Maresca's dismissal, but a Stekelenburg howler gifted the equaliser.
Zeman said: "We had done very well in the first half and unfortunately a mistake from the goalkeeper meant we conceded. It can happen and Stekelenburg is doing well overall, so there is no reason to suggest he won't start the next game.
"After that, though, we were unable to play with our heads. We should've tried to draw Sampdoria out to then find space.
"We created several scoring opportunities, but with another goal we could've created more space to hit the Blucerchiati. We started just throwing the ball forward with hope.
"In any case, I have nothing to complain about my team's performance. We had more than 20 attempts on goal."