Lost amid the “Venus and Serena” hype at the Family Circle Cup — the movie, Friday’s daylong Williams-fest, Saturday’s sisterly semis — was the continued breakthrough season of young Madison Keys.

Of all the young Americans who made an impact this week — five U.S. players under the age of 28 made the third round — none went further than the 18-year-old Keys.

Keys, from Rock Island, Ill., beat fellow American Bethanie Mattek-Sands on Friday to make the quarterfinals, her second quarterfinal run this season to go with a third-round appearance at the Australian Open.

But she didn’t have long to savor her achievement. Shortly after her straight-set win over Mattek-Sands, Keys had to face former No. 1 Venus Williams.

Venus won, 6-4, 6-4, to set up the semifinal showdown with sister Serena.

“(Friday was) bittersweet,” said Keys, who who was just 14 when she scored a 5-1 victory over Serena in a World Team Tennis match. “Quarterfinals, and then lose like two hours later. But I’m just taking a lot of good things about this tournament as well.”

As well she should. Keys impressed Venus in their match.

“She’s very talented,” Venus said. “And she’s just, at this point, learning the ropes and playing the matches. She needs more experience against the top players, because she hasn’t played as many top players yet. I think it’s just a matter of time for her.”

And that’s one thing Keys, and her fellow young Americans, have plenty of.

“There’s a bunch of younger players right now that are really starting to do well,” she said. “They are getting at least first round, second round, sometimes third round. So I think it’s great, and we are all kind of rooting for each other.”

All about the clay

Serena Williams has won 13 straight matches on Billie Jean King Court. No wonder it’s one of her favorite places.

“I love playing this court, I love this tournament,” she said after defeating sister Venus on Saturday. “I think it’s a good clay court. Sometimes you play on certain clay courts and they are not good and they’re funny and you can’t really slide, and it’s just weird. This one is a really good one, particularly this year, the last two years.”

Serena vs. Venus

More on the rivalry:

Serena has a 12-5 lead over Venus in finals and semifinals; Venus leads 5-2 in other matches.

The sisters have played three times when one was ranked No. 1 and the other No. 2. Serena won all three.

Net cords

Today’s doubles final will begin at 11 a.m. on Billie Jean King Court, followed by the singles final at 1 p.m.

Today’s singles final will be televised on ESPN2, with Cliff Drysdale and Pam Shriver on the call.

Three of four semifinalists on Saturday were former Family Circle Cup champs. Serena won in 2008 and 2012, Venus in 2004 and Jelena Jankovic in 2007.

Attendance

The crowd of 9,538 for Saturday’s Venus vs. Serena semifinal was the largest for a single session since the Family Circle Cup moved to Charleston in 2001. The previous record was 9,336 for a Friday day session in 2008, when Serena played Maria Sharapova in the quarterfinals. Serena won that match, 7-5, 4-6, 6-1.