In Saturday’s first semifinals of the Family Circle Cup Serena Williams(1) defeated Venus Williams(5) again; 6-1, 6-2. Although Serena appeared to breeze through the match effortlessly, she said that the match was more challenging than it appeared.

“When I play Venus, it’s never an easy opponent,” Serena said. “She’s my toughest opponent I’ve ever played, and I think she’s beaten me the most of any player.”

Serena’s win over Venus marks her 14th win against her older sister; 14-10 overall, and 1-1 on clay.

Outside of her occasional competitions with elder sister Venus, Serena has developed a rivalry with the Serbia native Jelena Jankovic(9).

Back in 2008 Serena beat Jankovic for the US Open title, winning in two straight sets 6-4, 7-5. During the 2012 Olympics Serena defeated Jankovic 6-3, 6-1 in the first round.

But in 2010 Jankovic reigned victorious over Serena when she came back from a first set deficient of 4-6 and won the second and third sets 6-3, 7-6 (7-5). The two-hour and forty-seven minute match marked one of the longest matches of Serena’s career. For Jankovic, defeating a Williams sister is a major accomplishment.

“I’m really proud of myself,” said Jankovic in response to the defeat. “[Defeating a Williams] doesn’t happen too often.”

In Saturdays second semifinal of the Family Circle Cup Jankovic struggled to defeat the unranked Swiss player Stefanie Voegele, eventually winning two sets to one; 6-4, 6-7, 6-2.

Jankovic will face Serena in the finals on Sunday; the winner will take a 3-1 lead in the four match series.

In reference to the 2010 match, Jankovic admitted to losing focus against the intimidating number one seed. “I just had to regroup and refocus,” Jankovic said after defeating Serena. “I didn’t want to waste my energy – and that’s what I basically did.”

Serena’s biggest disadvantage is injuries. During previous matches against Jankovic Serena was returning to tennis after knee injuries and wasn’t as physically prepared as she should have been.

“I wasn’t playing the points right. I feel like I should have won, could have won,” Serena said after being defeated by Jankovic in 2010. “I think I had an apple in my throat, but it is what it is. I can’t beat myself up over it – I just came back.”

Now that Serena is healthy, temporarily losing focus isn’t an option for Jankovic. Serena is frequently the number one seed because of her consistency and ability to readjust to matches after injuries.

Jankovic can pull of an upset if she wins Serena’s serves, has no flat serves, and commits little to no forced errors. But all of which are close to impossible against a player like Serena who has powerful serves and frequent acing streaks.

Serena will be challenged by Jankovic in the finals but not defeated.