England piled up 323 for eight, their highest ever total against South Africa, with Owais Shah, Paul Collingwood and Eoin Morgan all lashing half-centuries.
Shah top-scored with 98 off 89 balls, including six sixes, while Collingwood scored 82 off 94 deliveries and Morgan belted 67 off just 34 balls.
"It's the best England batting performance that I can remember. Obviously our confidence was low after the Australia series, but we just wanted to make sure we showed what we can do in this tournament. We didn't want to die wondering.
"We can play the shots, we have the skills, but sometimes it's just a mindset thing. We wanted to loosen the shackles and take the game to them," Strauss told a news conference.
"Owais took control clearing the boundary that many times, it was an absolute gem of an innings. He was well-backed by Collingwood and Eoin Morgan was tremendous at the end again. It was a fantastic batting performance."
Strauss defended his decision to deny opposite number Graeme Smith a runner in the closing stages of his heroic century.
"He asked me for a runner because he was cramping, but the umpires weren't particularly keen, I thought they were very uncomfortable with it and I didn't think he merited a runner.
"Cramping is about preparation and conditioning and at the end of a long innings you are going to get tired, it happens normally. But I didn't feel he was cramping that badly because he was still able to run," Strauss said.
South Africa captain Smith bemoaned a sub-par performance by his bowlers.
"The pitch played really well and you need to be consistent on those sort of surfaces. There also wasn't much spin out there, but it's hugely disappointing that we conceded more than 300," he said.
"We need to look at aspects of our attack when a pitch plays that well. We bowled three or four good balls an over, but two bad ones every over too."
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