Roy Hodgson's men fell to defeat in Manaus to kick off their Group D campaign in disappointing fashion, although England did produce 18 shots on goal - eight of which were on target - and scored via Daniel Sturridge.
Jagielka said he took plenty of heart from his side's positive performance, despite the scoreline not going in their favour.
"This is international football and, especially in a World Cup match, unless you do not concede and score goals, you will not win games," Jagielka said.
"That is the obvious way of looking at it. But if you take a step back and look at the performance as a whole I think there were positives, but the result makes these last two games that little bit more interesting."
England take on Uruguay on Thursday, before a group finale against Costa Rica on June 24, and Jagielka said it was important for him and his team-mates to try and qualify on their own terms.
"Mathematically, there could be a draw and then a high-scoring win in the final game but, if we want it in our own hands and we want to qualify in a little bit of style, we want to win these last two games," the Everton man said.
"If we take away the result and look at some of the performances, the exciting players we had out on the pitch, the future is looking good but we have still got to do well in the present.
"If we had lost and not gone for it and scored goals or created chances, these next two games would have looked bleak.
"Once we recover and look forward there will be a lot of positive things, and hopefully the camp will be confident to put in some good performances."
Jagielka could be tasked with keeping Merseyside rival Luis Suarez quiet when England face Uruguay, providing the striker is declared fit enough to play.
"I do not think Uruguay are a one-man team. It would be disrespectful to say they are putting all their hopes on Suarez," Jagielka added.
"They are in a pretty similar situation to us now (after losing 3-1 to Costa Rica). I presume the game will be exciting and both teams need a win.
"I think confidence-wise we will have more, particularly if the attacking boys keep playing as well as they did and take our chances."
