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.
Nadal told reporters after the match that returning to top spot had capped "a great year, one of the best years of my career without any doubt".
"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."
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.
The world No. 5 told reporters after the match that he suffered a back injury when he reached for a shot. "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."
Berdych then praised Nadal's achievement on reclaiming the top spot. "With Rafa, well, just all the credit. It is really incredibly well done in the whole short time that he has become a number one again," he said. "That's really an achievement for an athlete like him."
Nadal was sidelined for the second half of last year with a knee injury and is unbeaten since he crashed out of Wimbledon in the first round in June. He has twice finished the season as the top ranked player, more recently in 2010, and the first time in 2008, after he edged into the top position by winning gold at the 2008 Beijing Olympics.
The 27-year-old, tipped to eclipse Roger Federer's record of 17 Grand Slam titles, has won 10 ATP World Tour titles in 2013. Tennis legends Andre Agassi and Pete Sampras reportedly said Nadal could overtake Federer before he finishes his career.
Nadal believes he would need to sustain his form — and crucially his fitness — for the next four years if he is to better Federer's Grand Slam achievements. The current game is said by tennis pundits to be dominated by the 'Big Four' — Nadal, Federer, Djokovic and Briton Andy Murray.
However, Nadal is emerging as the dominant force and he has had the beating of Djokovic, coming out on top at both the French Open and US Open, as well as the Canada Masters. Djokovic has previously warned Nadal that he will not give up the top spot without a fight. "As long as there is a chance, I will fight for that top spot," he said ahead of the dual ATP and WTA event, which is being staged at Beijing's Olympic Park.
Roddick had Djokovic pinned up against a locker in 2008
Los Angeles: Retired American tennis player Andy Roddick has lifted the lid on his feud with world number one Novak Djokovic, revealing the two players almost came to blows in a locker room bust-up.
Roddick said he pinned Djokovic up against a locker in the US Open dressing room after Djokovic "beat the pants off him" at the final major championship of the ATP tennis season. Roddick, 31, did not say when the incident happened but the two had a very public row during the 2008 US Open. "I won't say his name, I'll just say it rhymes with 'Schmovak Schmokovic'," Roddick said on a panel discussion on the American sports network Fox.
"We got into it at the US Open one time," Roddick continued. "I was kind of talking trash and he came out and beat the pants off of me as he would. But then he kind of chirped afterward and he came straight in, I went right up to him and had him up against the locker, but then I realised his trainer was about a little bit bigger." Roddick, who retired after the US Open, said. "I kind of checked myself. My trainer is about five-foot-eight, 130 [pounds] ... I kind of backed off real quick. I was about to get railroaded from the side."
Roddick is a former world number one tennis player whose only major championship came at the 2003 US Open. Serbia's Djokovic, who is one of the most well-liked players on the ATP Tour, has six grand slam titles, including four Australian Open crowns.