LEXINGTON, KY, USA - Top seed Serena Williams overcame a stern test from elder sister Venus to reach the quarterfinals at the inaugural Top Seed Open presented by Bluegrass Orthopaedics, 3-6, 6-3, 6-4.

"I've lost a few tight sets lately, so I was telling myself I really wanted to win this one and try to focus on those last two games," she said in her on-court interview.

Serena rallied from a set down and 4-2 final set deficit to defeat the five-time Wimbledon champion for a 19th time in a thrilling two hours and 19 minutes on Center Court.

"I'm super relaxed. Having no crowd sort of makes things more relaxing. I've practiced in louder places than this court!"

The Williams sisters' WTA rivalry spanned into a 31st match and fourth decade on Thursday, facing off for the first time since the 2018 US Open, where Serena won in straight sets en route to the final. 

Venus was fresh off her first match win of the season over fellow former World No.1 Victoria Azarenka, having fallen in the first rounds of both the Australian Open and Abierto GNP Seguros to Coco Gauff and Kaja Juvan, respectively.

Serena began 2020 with a 73rd career WTA title, and first since the 2017 Australian Open (where she defeated Venus in the final), after which she married Alexis Ohanian and gave birth to daughter Alexis Olympian Ohanian Jr. Her three-set win over fellow American Bernarda Pera was the first time the 23-time Grand Slam champion had been in action since helping lead the USA to a Fed Cup victory over Latvia.

2020 Lexington highlights: Serena serves out sister Venus

Leading their WTA head-to-head 18-12, Serena took the quicker start in Kentucky, breaking to start the match and navigating a tense first service game to consolidate.

From there Venus, who has been tinkering with the serve motion that once helped her hit the second-fastest recorded delivery at the 2007 US Open (129mph), went on a tear, roaring through the next six of the next seven games to serve out the opening set.

Looking to force their first three-setter since the 2015 US Open, where Serena extended her Grand Slam winning streak to 26 straight in the hopes of capturing a Calendar Year Grand Slam, the top-seeded younger Williams tightened up her service games and began to push Venus on return, securing a crucial break after a long sixth game. A forehand error from Venus soon leveled the match.

The final set saw Serena take an early break lead, only for Venus to wrest momentum in surprising fashion, reeling off the next three games to put herself two games from a first victory over her sister since the 2018 BNP Paribas Open.

Serena responded by taking a 0-40 lead of her own in the following game, taking the next three games and moving ahead 5-4 with a stunning backhand winner.

Serving out the match on her first match point, Serena will next face either countrywoman Shelby Rogers or rising Canadian star Leylah Annie Fernandez for a spot in the semifinals.

"I honestly didn't come here to win. For the first time in my career, I came here to win some matches and see what happens. I haven't had this much time off since the baby, so now I'm just trying to get some rhythm and see what happens."