Stosur sealed the victory on her second match point when the Russian sent a shot wide.
Stosur won her second title of the season and fifth of her career in Osaka, Japan, last Sunday. The Australian was runner-up to Caroline Wozniacki here last year.
The 18th-ranked Halep, who has won the first four titles of her career this season, jumped out to 4-0 in both sets against Pavlyuchenkova. The Romanian sealed the victory on her second match point when Pavlyuchenkova double-faulted.
"The score, it looks like it was very easy, but it wasn't," Halep said. "I moved very well and I hit the ball very strong. She didn't move very well. I'd like to win my year's fifth final but it will definitely be a hard task as Samantha is a top player in good form."
The 10th-ranked Gasquet, still vying for the eighth and final spot in the ATP Finals next month, constantly beat Karlovic's serve-and-volley play with passing shots, and broke the Croat once in each set. The Frenchman served a winner to close the match.
"When you are playing with a hard-server like Karlovic you should be very careful when you get a chance to break," Gasquet said. "Today, I had only two break points and I managed to convert both. Meanwhile, I managed to save a break point on my serve and that made the difference."
The 102nd-ranked Kukushkin and Seppi traded sets before Kukushkin took a 4-1 lead in the decider and served for the match at 5-3. Seppi broke back only to fall 40-love down on his serve in the next game. Kukushkin broke again when the Italian sent a shot into the net.
"I haven't played in an ATP semifinals or finals for three years, so I desperately wanted to win," Kukushkin said. "In the tight end of the third set I had a stronger desire to win and it decided the match."
Kukushikin reached his first final since winning his only title in St. Petersburg in 2010 and is the first qualifier to reach the final in Moscow since Paul-Henri Mathieu won the title in 2002.