Pietersen gave his team a useful total with some impressive strokeplay
England maintained their winning run in the Stanford Series, beating Trinidad & Tobago by one run in the final warm-up.
Their plans were hit by a stomach bug that sidelined Stuart Broad, Luke Wright, Ryan Sidebottom and James Anderson, leaving just 11 fit players.
But Ian Bell made 37 and skipper Kevin Pietersen hit three sixes in an assured 44 from 30 balls in a total of 141-6.
Paul Collingwood took 2-12 but three were needed off the final ball and Ravi Rampaul was run-out chasing a second.
So England go into the $20m crunch contest against the Stanford Superstars with two wins, but will hope to have more than 11 to choose from on Saturday.
Sidebottom and Anderson would have been left out in any case to accommodate Steve Harmison and Graeme Swann, but there was no intention to bring Alastair Cook in to bat at number nine.
That was not the only problem. The pitch had a distinct ridge at one end, and it duly produced some erratic bounce when England were asked to bat first.
Andrew Flintoff is on his last legs, so it is just a case of getting the boys right for Saturday now. The lads are just not feeling special at the moment
Bell's method of combating it was to step down the wicket and he did so effectively to cut Rampaul for the first boundary in the fourth over.
Matt Prior failed again at the top of the order, making four from 10 balls, although the ball from spinner Sherwin Ganga which he cut to the keeper did bounce excessively.
Samit Patel was elevated to number three, and he took successive fours from Richard Kelly's loose opening deliveries.
Leg-spinner Samuel Badree, who again bowled the first over, returned with a googly that bowled the all-rounder who was guilty of missing with a horribly agricultural mow across the line.
Pietersen looked in excellent touch, however, even displaying the switch hit. And though that stroke did not bring him a boundary there were plenty of others that did, an awesomely powerful smash over wide long-on for six followed by a thump down the ground for four off a full toss next ball.
All bar the final high catch of the innings were safely taken by England
There was a good deal of flexibility from England in the field as well, slow left-armer Patel taking the first over and Swann replacing him to bowl the third.
But Flintoff for once struggled with his line and was down the leg-side with his first three balls that all went to the boundary.
Collingwood's wicket-to-wicket seamers accounted for Lendl Simmons trying to sweep and Flintoff atoned in his next over with the important wicket of free-scoring Darren Bravo, Harmison taking the top-edge safely with his fingers pointing upwards moving in at third man.
England had reduced their opponents to 70-4 after 12 overs and should have taken the fifth wicket in the next when Patel dropped a chest-high return catch that he initially appeared to have taken.
Again it was wicketkeeper Denesh Ramdin, surely playing his way back into the minds of the West Indies selectors, who took command of the situation.
Following his 41 from 28 balls that helped to defeat Middlesex on Monday, the compact right-hander played some more innovative shots in his 37.
England had to call on Middlesex's Dawid Malan to act as 12th man, and he was forced to take the field, in Prior's spare shirt, when Shah jarred his knee in the sodden outfield.
He returned but Flintoff tumbled over in his delivery stride and also left the field suffering from the stomach bug as 28 were needed from the final 18 balls.
Ramdin flicked a simple catch to backward square-leg off the final ball of the 18th over, but just when it seemed England had solved their catching concerns, Bell dropped a straightforward chance coming in from long-on as the tension increased.
I think we will have to play a couple of spinners. I will just try to keep my cards as close to my chest as possible
Flintoff returned to trap Kelly bang in front for his third wicket, but did not look comfortable and headed for the pavilion again after completing his final over.
Harmison bowled the final over with 10 needed to win, and after some good ones in the blockhole, Badree moved across his stumps to glance a boundary.
The prospect of the Stanford Super Over - a one-over match with a new toss - was imminent but Shah kept his calm fielding on the boundary and collected quickly before sending a low return to Prior, who also held his nerve admirably and whipped off the bails.
Pietersen said afterwards: "We definitely thought we had enough [runs] but we have got four guys sick at the hotel and another couple who are not well tonight.
"Andrew Flintoff is on his last legs, so it is just a case of getting the boys right for Saturday now. The lads are just not feeling special at the moment.
"But I am sure there will be not many missing the bus on Saturday."
Ramdin said: "When Flintoff bowled three dot balls and got Richard out that is when the game changed because we were under pressure again. Up until then I thought we would win."
Pietersen, suggested both Swann and Patel will play on Saturday.
"I think we will have to play a couple of spinners," he said. "How I use them I am not 100% sure yet. I will just try to keep my cards as close to my chest as possible."
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