Against Bertens, she got in just 54 percent of her first serves and won just 63 percent of her first-serve points, leading to four breaks for her opponent.
She bested Zarina Diyas in straight sets in her opener, a round that Venus didn't even play in due to being seeded and getting a first-round bye.
Venus closed out the 29th career meeting between the two on her second match point as Serena sailed a forehand long to end the third round match. When she entered the court, she was given a loud ovation from the packed arena, with many in the stadium standing and applauding her third appearance in IndianWells in the last 17 years.
INDIAN WELLS-It wasn't magnificent tennis, by any stretch. "As long as I'm moving forward, even if it's at a turtle's pace, I'm OK with that".
It was an unfamiliar situation for Serena, with Venus responding to everything thrown at her, including a pair of break points, which she saved. First of all, 17 years ago seems like forever ago.
The match is scheduled to start around 10 p.m. ET and will be broadcast on the Tennis Channel.
The sisters last met in the 2017 Australian Open final, when Serena won her 23rd Grand Slam singles title.
If you've been following Serena then you know she has always been killing it with her looks. Let us know what you think about Serena Williams Taking on the beauty industry in the comment box below!
Venus, seeded eighth, reached the Wimbledon final, the US Open semi-finals and the championship match of the WTA Finals while Serena was away from the tour.
"I still have a lot to give".
The 23-year-old Svitolina advances to the third round where she will face Spaniard Carla Suarez Navarro who beat Hsieh Su-Wei, of Taiwan, 6-4, 2-6, 6-3.
In an essay for Time magazine just before her return, she made it clear she feels much of the vitriol was racist in nature. I never lost a match sitting down.