You have to feel for Angelique Kerber.

Here she is in her prime -- she turned 29 in January -- ranked No. 1 in the world, and she just can't shake the Williams sisters.

Serena Williams, with whom Kerber split two Grand Slam finals in 2016, is 35 years old. Serena's knee acted up following a championship run at the Australian Open and she elected to sit out the Indian Wells/Miami gantlet.

Advantage, Kerber, right?

Not necessarily. Venus, who turns 37 next month, is her quarterfinals opponent Wednesday at the Miami Open.

Kerber is a more-than-credible combined 6-8 against the Williams sisters, bringing to mind the great rivalry they had against Martina Hingis back in the day. The five-time major champion was a sterling 17-17 against the sisters. Those five titles came in a three-year span from 1997-99, and it's hard to believe Hingis, 36, was born five months after Venus and one year before Serena.

Venus Williams has lost four of her past five meetings against Angelique Kerber. Geoff Burke-USA TODAY Sports

The head-to-head for Kerber against Venus is an encouraging 4-2. After a loss at the 2009 Australian Open, the German has won four of five, although most of the sets have been highly competitive.

Kerber has scuffled this year, at least by her new, higher standards. She was 9-6 entering Miami, but has played her best tennis of the year, beating Shelby Rogers and qualifier Risa Ozaki in the past two rounds.

After losing to eventual champion Elena Vesnina in the fourth round earlier this month at Indian Wells, Kerber was asked if it was tough to match those breakthrough 2016 results.

"I'm not looking back on the tournaments," she said to the media in Miami earlier this week. "It's a completely new year, new tournament, and every tournament starts from zero.

"For me, I think I get used to the pressure and everything. This is what counts for me. I'm not comparing this year to the last years."

So what can Venus learn from Serena's 6-2 head-to-head advantage over Kerber?

When Serena is healthy, she has a more diverse game than Venus and that flexibility has given Kerber difficulty. Venus has a less nuanced approach -- she hits low, flat groundstrokes and her longer reach helps her track down balls that helps compensate for her more limited movement. Her margin for errors is far less than Serena's.

Venus' state of mind can usually be discerned within minutes. If she's on edge and spraying balls, Kerber should have the upper hand. She remains the game's best defender and thrives against attacking players. But, if Venus is hitting her spots, using her power, shot-making ability and volleying skills, it should be a semifinals berth, opposite the winner of No. 3 Simona Halep and No. 10 Johanna Konta.

Patience, not always a Venus attribute on the court, could prove to be the deciding factor.

Roger Federer, still slamming at 35, has been the story of the year in professional tennis. But step back and consider the continuing wonder of Venus. It's a tribute to her spirit that her energy-draining Sjogren's syndrome has become something of a footnote.

Told Sunday that she was (again) the oldest player in the Miami draw, Venus had the good grace to smile.

"Yeah," she said, "2020 here I come."

The way she's playing, she might not be kidding. Venus reached the Australian Open final and the quarterfinals at both Indian Wells and Miami. Only Karolina Pliskova and Caroline Wozniacki matched her in both of those North American Premier Mandatory events.

This is Venus' fifth tournament of the year, and she's 13-3.

After the Aussie Open, both sisters spoke of the inspiration they had received from the other.

"Venus and I work so hard," Serena said at the time. "Still, to this day, we work side by side each other at practice. We motivate each other. The motivation she gives me, it's really second to nothing."

At this stage of her career, one Grand Slam title behind Margaret Court (it's 24-23), Serena can learn from Venus' exceptional perseverance.

Said Venus: "To have this opportunity to play against each other again, to be able to rise to that occasion, was quite momentous.

"Ready to kill it this year. That's my goal."