Venus Williams has won seven Grand Slam singles titles in her career.
Williams will now face Johanna Konta who defeated Simona Halep to become the first British woman to reach the Wimbledon singles semi-finals in 39 years.
Desperate to keep tennis's most famous trophy in the family, Venus Williams insists age is merely a number as she closes in on a sixth Wimbledon crown a month after her 37th birthday.
Having stunned the tennis world by becoming the first unseeded player to win the French Open, Ostapenko is in her first Wimbledon quarter-final as she rides an 11-match winning streak at the majors.
"It was for sure the best match for a long time for me", Kerber said in defeat.
She meets the victor of Johanna Konta and Simona Halep in the semis.
The Lavitain, known for her big-hitting play, did make a tough match in the second set and took it all the way to 5-5 before Venus, who won last Wimbledon in 2008, sealed it 7-5 when Ostapenko send her forehand service return wide.
While Williams was strong on her serves, Ostapenko struggled with her backhand shots.
The men's quarterfinals Wednesday: Djokovic against Tomas Berdych, Roger Federer against Milos Raonic, defending champion Andy Murray against Sam Querrey, and Marin Cilic against Gilles Muller, who stunned Rafael Nadal in a marathon that ended 15-13 in the fifth set Monday.
After repeatedly digging himself out of hard situations, Nadal finally succumbed, broken in the last game of a 6-3, 6-4, 3-6, 4-6, 15-13 loss to Muller on Monday.
The same could not be said for Venus, though, who snubbed the same gentleman after her win over Jelena Ostapenko.
The other semi-final will pit 2016 French Open champion Garbine Muguruza against surprise package Magdalena Rybarikova.
Williams is getting better as the tournament progresses and the quality of opposition supoosedly steps up - she has not dropped a set in her last three matches at SW19.
Williams simply cranked things up a notch, broke the now completely bowed Ostapenko one more time, then served out comfortably.
"She says, 'I love my job!' and she means it".
Kim Clijsters won her doubles match with Rennae Stubbs, while former men's champion Richard Krajicek was celebrating again alongside Mark Petchey. Venus played really well and very smart. Ostapenko returned and that gave Williams the break to tie the set.
Venus added: "When you're out there, all you're thinking about, especially at least on my side, all I can control is myself". She missed the second half of last season after wrist and knee operations, and her ranking fell out of the top 400. "I did that and feel fortunate to have taken a few of them". She was the first woman to win her debut tour-level title at a Grand Slam tournament since 1979. Of course I'm disappointed that I lost the match, because I was really playing good.