Tiger Woods and company are preparing themselves for a dramatic finale to the U.S. Open this year.

Defending champion and world number one Woods has earmarked the 17th and 18th holes at Olympia Fields as potential key moments in the battle for the 103rd Open, which begins on Thursday.

"If you're making pars on the back nine, I'm sure you'll probably gain ground because there are some holes out there where you can make one mistake," Woods told reporters at the country club in the south Chicago suburbs.

"That is, 17 and 18 are probably two of the most difficult golf holes we play on the entire course -- they happen to be back-to-back and they're the last."

Critics regard the par-70 Olympia Fields course as something of a chore, disappointed that the back nine contains no par-five tests.

But organisers hope the potential exists for prime time television excitement when the last round reaches a climax around 1900 CDT (0000GMT) on Sunday evening.

"The par-fives are over after the sixth hole, but every course is different," said Fred Ridley, United States Golf Association (USGA) vice-president and championship committee chairman.

"But there are certainly enough challenging par-fours coming in and, of course, the 17th hole, which is a heck of a par three.

"We feel really good about the finish for the last round."

Kenny Perry, the 42-year-old American, managed to sum up the challenge facing him and his peers on the eve of the major.

"The stretch is going to be on from the back nine," he told reporters.

"The 17th is a 200-yard par three, and the 18th is very difficult.

"It's one of the hardest finishing holes, with the green severe, sloping from back to front. (The last two) are really going to determine (the outcome).

"Whoever plays those two holes the best will probably win the golf tournament."