Serena Williams expects Venus to be the crowd favourite when the sisters clash in the fourth round of Wimbledon on Monday.

World number one Serena, who has already collected the Australian and French Open titles this year, survived a third-round scare as Britain's Heather Watson served for the match with the backing of some boisterous Centre Court support.

The 33-year-old acknowledges that a victory for her elder sibling, the 16th seed, would be popular in light of the latter's battle back towards the summit of the women's game after being diagnosed with Sjogren's syndrome in 2011.

The autoimmune disease, which can cause fatigue and joint pain, forced Venus onto the sidelines and her ranking plummeted to 103 in the world before a sustained effort hauled her back into the top 20 last year.

"I expect more people to be rooting for Venus," said Serena. "I would be rooting for Venus. 

"She's been through so much. She's had a wonderful story. She's been so inspiring to me.  

"You know, she's just an incredible individual. She's just so amazing. She's been so inspiring to a lot of people with the same things that she goes through, too."

Ahead of their first grand slam meeting for six years - the previous encounter coming in the 2009 Wimbledon final when Serena triumphed - the younger Williams holds an overall career head-to-head advantage of 14 wins to 11.

"You just have to be focused - there's no easy points against Serena," said Venus.

"I think no matter how Serena's playing, she knows how to win."