The Spanish world number two only needed to make the final in Beijing to edge ahead of Novak Djokovic in the new rankings, which will be announced by the ATP on Monday.
Nadal, who last topped the rankings in July 2011, has enjoyed a remarkable season, returning from injury to dominate the hardcourt tournaments.
He will overtake defending China Open champion Djokovic at the top, even if the Serb overcomes France's Richard Gasquet in his semi-final later Saturday and retains the title on Sunday.
"Sure is special be back to the top position of the ranking after more than a half year without playing tennis," he added. "I felt during all the season very excited every time I go on court."
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Djokovic is currently on his 101st week as the top-ranked player.
Czech Berdych pulled out of his semi-final after receiving treatment for an injury with Nadal leading 4-2 in the first set.
Nadal had broken Berdych's serve in the fifth game after the pair appeared to be matching each other competitively in the early stages.
"I don't know actually what happened," he said, adding: "Just the pain was there. That's it. I mean, before I didn't feel anything. I was completely fine. I just had no problem at all. Nothing.