South Africa-born batsman Pietersen, despite suffering a bruised left knee when hit by pace bowler Lasith Malinga, struck a typically dashing 73 at The Oval on Tuesday but that was not enough to prevent England going down to a convincing 46-run defeat.
That loss, England's 12th in their last 16 One-day Internationals, saw them go 2-0 down in the five-match NatWest Series ahead of Saturday's match at the Riverside after an equally emphatic reverse at Lord's last weekend.
England, had they been in a better position, might have considered resting Pietersen - who sustained a left knee injury during the final match of their 5-1 One-day series defeat in India - for what is now a must-win game if they are to keep the Sri Lanka series alive.
But with the likes of Michael Vaughan (knee), Simon Jones (knee), Ashley Giles (hip), Andrew Flintoff (ankle) and James Anderson (back) all still injured, Pietersen said it was important he turned out at the Riverside, the home of north-east county Durham.
"We've lost Flintoff, Giles, Jones, Vaughan and Anderson so if I went down as well it's not going to help matters is it," he explained.
"I think it's pretty important that I do play on Saturday and I want to play because I hate missing games."
And Pietersen added he felt he was carrying greater responsibility with so many senior players sidelined.
"There's no Vaughan and there's no Flintoff and it does play on my mind a little bit, but then again I seem to go okay under pressure and I don't mind that, I don't mind putting that extra bit on me.
"I had some extra throw-downs before the game at The Oval to make sure I got into the groove of playing straight and trying to get myself some runs. I scored 73, but it's not really good enough, to be fair."
In the meantime Pietersen said it was unrealistic to expect all of England's newcomers to take instantly to limited overs internationals.
And he pleaded for patience on behalf of Lancashire seamer Sajid Mahmood, whose Oval figures of 7-0-80-2 provided the third most expensive seven-over analysis in one-day international cricket.
"It's a learning curve," said Pietersen. "Sajid went for 80 runs but I got out for 10 at Lord's on an absolute belter of a wicket and you learn from your mistakes.
"He's only played a handful of one-day internationals and it's a process. I had to learn, Marcus Trescothick would have had to learn, Ricky Ponting would have had to learn - everyone in an international team doesn't come in and just hammer it all day every single day."
And he pointed to South Africa all-rounder Jacques Kallis as an example of patience rewarded.
"Some people take longer than others. I remember Jacques Kallis at the start of his career. He didn't come in and blitz the world but the bloke now averages mid-50s in Test match cricket."
He added: "I don't think the new (England) players are down, but what will tell is how they come back after three, four or five of these games.
"We're 2-0 down and it will be interesting to see how we go now we have to win the three remaining games."
England coach Duncan Fletcher, despite his team's form, has given the players two days off before training resumes on Friday at the Riverside.