Klaasen, fourth in the ICC's world rankings for batsmen in One-Day Internationals, scored 64 off 56 balls on Saturday to help South Africa qualify for the Champions Trophy semi-finals with a seven-wicket win over England.
"I gave myself a challenge with (South Africa head coach) Rob Walter this trip. I want to be the best in the world," Klaasen told Sky Sports after the match in Karachi.
"I know I can play situations well and for me, just to keep hitting it on the ground for as long as possible, like I did tonight" is important.
"I'm quite pleased with my innings tonight... standing still and just trusting my technique. I know my swing is good, so as long as it clicks, then I'm quite happy."
South Africa will play India or New Zealand in the semi-finals on Tuesday or Wednesday.