Venus Williams is just about the perfect older sibling: She supports Serena endlessly, protects her fiercely and even lets her pick which bedroom she wants when they’re on the road.

Where does Venus draw the line? At Grand Slam championships.

The sisters face each other again in a major final, meeting Saturday for the Wimbledon title for the fourth time.

“I’m happy for her to be in the final, but I have to face her and defeat her,” Venus said after reaching her eighth final at the All England Club by routing top-ranked Dinara Safina 6-1, 6-0. “I don’t necessarily want her to lose, but for sure I want me to win.”

After their showdown, the sisters become teammates for the doubles final, where they are the defending champions.

Besides having won five Wimbledon singles titles, beating Serena in last year’s final, Venus is trying to become the first woman to win three straight championships since Steffi Graf from 1991-93.

“Even if she’s not playing her best, just that fight she has, you’re facing that,” Venus said. “So there’s so much to face when you play her. It’s definitely a lot to get your mind around.”

Serena showed her fight Friday, saving a match point against Elena Dementieva before winning 6-7 (4), 7-5, 8-6. The match, longer by time than any Wimbledon women’s semifinal or final on record, was one of the most exciting of this year’s tournament.

But if that was tough, wait until Serena faces an opponent that has won 20 consecutive matches on Wimbledon’s manicured lawns, the last 17 in straight sets.

“You know, it’s not the easiest opponent on grass,” Serena said. “I hope I win. Obviously, if I do, I’ll be really, really excited. So we’ll see.”

Off the court, the sisters often share an apartment for Wimbledon, and sibling rivalry doesn’t really come into play when it comes to choosing the better room.

“I always defer. She picks first,” said Venus, noting that back home in Florida their rooms are the same size. “It makes me happy. You know, I want her to pick.”

On the court, things get more intense when they’re on opposite sides of the net.

“I feel very calm, actually,” said Venus, who is 2-5 against Serena in Grand Slam finals. “But, of course, I’m going to bring the tough feet to the court.”

For Serena, it’s just more of the same.