World No.3 Pegula, the 32-year-old who won her first WTA title in Washington in 2019, is seeking her third title of the year and 12th of her career after winning in Dubai and Charleston.
The 22-year-old Shnaider, who reached this year's French Open semi-finals, was bidding for her sixth WTA title and raced into a 5-2 lead in the opening set before Pegula began her comeback by holding serve and breaking in the ninth game.
The American then held to love for 5-5, broke again in the next game and served out the set when Shnaider sent a forehand wide.
Pegula broke for a 3-2 lead in the second set and extended her advantage to 5-2 with another break, before closing out the match with a forehand winner after 87 minutes.
"I just capitalised on a couple of areas," Pegula said.
"I think I started just trying to find the rhythm on the return. I didn't think I was that far off ... So, just trying to pick up my energy and again, try and be a little bit more aggressive."
Eala moved within one win of her first WTA title after delivering a composed performance against four-time grand slam champion Osaka.
The 21-year-old, playing in her third semi this year, reached the last four after beating second seed Elina Svitolina for her sixth win of the season over a top-10 opponent.
Eala, who made the fourth round at Wimbledon last month, broke Japan's Osaka in the ninth game of the first set, then held to love to take the opener.
She carried that momentum into the second, breaking in the opening game and again to move 4-2 ahead before sealing victory without dropping a set during her run to the decider.
"I think I played really well and, of course, it's such a meaningful match against a great player. So really happy to share the court with Naomi," Eala said.
"I'm in the final for a reason. I just have to trust myself.
She (Pegula) is such an amazing player. I think it's going to be a really good match."
8°C