The Blues twice surrendered the lead against the Ukrainians before Victor Moses headed Juan Mata's corner home in stoppage time minute to clinch victory.
But the Spaniard believes the west London outfit must improve if they are to avoid defeat later in the competition.
"I'm happy with the result but we know we must do much better,” Torres told Sky Sports.
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"We know we have to improve. We have been creating problems for them, pressing and creating chances from their mistakes, but not when we have the ball like we're used to.
"This kind of situation cannot happen again because, especially in the Champions League, at times like these you can be out."
The striker was also quick to praise the never-say-die attitude in the dressing room, citing his team-mates' spirit as a huge factor in their triumph last season.
"When we needed to win, we did," he continued.
"We did it against Valencia, Napoli and Barcelona - also the final against Bayern Munich. This was really the first big test of the season and we did it as well.
“We were a bit lucky - I think maybe the draw was the more fair result - but Chelsea has this special thing that no-one can buy.
"That's good. We have to keep the good luck on our side."