When former Inter Milan coach Jose Mourinho returned to Stamford Bridge in the knock-out stages of the Champions League, both Petr Cech and Henrique Hilario were unavailable for selection through injury.
This led to Turnbull making his appearance in the quarterfinal defeat.
"It was such a massive match and there was so much going on building up to it," he told chelseafc.com, "it was just incredible.
"It was a big European night, Mourinho came back, the whole scenario around it was huge. It was such a massive game and it was a special one for me to be involved in.
"And the atmosphere for that game was one of the best of the season, just with all the anticipation that the fans must have felt.
"I know I keep saying it but it was such a massive night. It's just a shame we didn't win in the end."