Nicol David had to endure, adjust and even take a gamble as she reached her fourth World Open final on Saturday.

David struggled in many of the rallies against an impressive Alison Waters, and had to save four game points to avoid going down two games to one before eliminating the Englishwoman 4-11, 11-6, 13-11, 11-7.

At the 12-13 mark in one of the games, David made two unbelievable retrieves near the end of a long, long rally before closing the game with a saved point with an accurate cross court length.

"That's squash, it's all about working for every point," said Malaysian star David, who appeared unusually relieved after the final rally. "The third game was crucial and I didn't want to lose that."

But David admitted that she had had to change her tactics against an opponent she had beaten on all of their eleven previous meetings.

"I felt confident in the first three points but I was trying to do too much too soon," the world number one said.

"I had to forget that first game and get going again. I had to get ahead in the next game. I had to be very solid and to get the ball past her."

When David wasn't able to do that she quite often got punished by a player who was at times inspired on the volley and who hit some punishing drives which dragged her famous opponent around the court.

There was also a moment in the pivotal third when David betrayed her tension in an exchange with the referee after being denied a let when she collided with Waters and fell.

The world number one from Malaysia, renowned for her sporting attitude, nevertheless tried to make her case three times before being told that the decision had been made and that was that.

The pressure eased a little in the fourth game, in which David took the lead from the start, though Waters pegged her back to a one-point deficit in the middle of the game.

By then David was starting to hit the ball more punishingly herself, finding a power and an aggression which is by no means characteristic of her mobile counter-attacking style, and for the first time getting on top.

The result guaranteed a much hoped-for final between Amsterdam-based players, because earlier Natalie Grinham, the second-seeded Australian who now represents The Netherlands after marrying World Open tournament director Tommy Berden, also came through.

Grinham did that with a win over her elder sister Rachael Grinham, the third-seeded former world champion, proving physically stronger in a 11-13, 11-6, 11-6, 11-4 success.

This was not a physical game however, for the sisters produced yet another of the many masterpieces of lob-and-drop, drive and cut-off, angle and reverse angle, before the 33-year-old began to tire.

Rachael had had to come back form two games down in both her previous matches, against Vanessa Atkinson and Omneya Kawy, and these efforts almost certainly cost her.

"I always feel more tension when I play against my sister," said Natalie.