Sevastova is set to play the final against the victor of the match between Caroline Wozniacki of Denmark, the second seed and victor of the Australian Open this year, and wildcard Wang Qiang of China.
Sevastova, who has not beaten Wozniacki in five attempts, said was pleased with her performance this week despite missing out on a second title of the season.
"I'm just happy to have reached 30 today, I'm going to enjoy that", said Wozniacki, a former number one.
Her win means that she will stay at No. 2 in the rankings and Sevastova will rise to a career-high of No. 12.
For the title in Beijing, the Dutch competed with Anastasia Sevastopol, which is in the semifinals, defeated the US Open champion Naomi Osaka.
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Both players held serve until Sevastova handed Wozniacki a break with an ugly unforced error, sending a drop shot straight into the net, putting the Dane up 4-2.
"I was in a really good shape coming up to this tournament", Basilashvili said.
The 28-year-old Wozniacki, who won her maiden Grand Slam at the Australian Open at the start of this year, was imperious against the unseeded Sevastova, winning 6-3, 6-3. Sevastova put up some brilliant shot and failed to convert her first two break point chances as Wozniacki completed a big hold to 1-1.
However, at 3-3 Wozniacki produced a moment of magic to set up three break points with a superb backhand pass on the run before Wang double faulted, the Dane wasting little time in reeling off the next two games to earn a place in her 54th career final.
"I wasn't able to play with that fire that I have in all my matches", Del Potro added, saying however that 34th-ranked Basilashvili "played unbelievable".