The first momentum swing came mid-way through the first set - after Muguruza powered to an early 4-2 lead, Radwanska reeled off four games in a row to sneak out the 41-minute opening frame, 6-4.
Then, the big swing - Muguruza reeled off 11 of the next 15 games to not only take the second set, 6-3, but build a 5-1 lead in the third. The No.4-seeded Radwanska began closing in, winning the next three games in a row to make it 5-4, and she even had a point for 5-all, but it was just too little, too late.
The No.5-seeded Muguruza sealed the victory after two hours and 13 minutes on court, 4-6, 6-3, 6-4.
Muguruza had bigger and tidier numbers for the match - she finished the match with a -1 differential of winners to unforced errors (43 to 44) while Radwanska finished with a -3 differential (24 to 27).
"I know Aga is an amazing player, so I knew I had to be concentrated and focused all the time against her, and try to be more ready in the important moments, which was my goal," Muguruza commented.
"I'm extremely happy to be in the final. I'm really going to try and get the trophy."
Muguruza, who will now move from No.5 to a new career-high of No.4 on the WTA Rankings on Monday, is a win away from the biggest title of her career by far - the WTA Rising Star's only WTA title to this point came at the International-level event in Hobart right before the Australian Open last year.
Awaiting her in the final will be the No.12 seed, Timea Bacsinszky, who also rallied from a set down to pull off an upset in the first semifinal match of the day (watch highlights from that match here).
Muguruza has beaten Bacsinszky in both of their previous meetings, both of which came this year.
Radwanska, who would have qualified for the BNP Paribas WTA Finals Singapore presented by SC Global had she won Beijing, still has a chance to qualify - she's playing the Tianjin Open this week.
"I'm still chasing Singapore," the former World No.2 said. "So Tianjin, and Moscow, as well."