And although the 6 feet 2 inches tall Roddick has recorded the fastest serve ever at 155 miles per hour, the 6 feet 10 inches tall Karlovic, the tallest player ever on the ATP Tour, is an ace machine.

Roddick leads the Croat head to head 3-1 and won the two players' last meeting at the Washington semifinals in 2007. However seven of their ten sets contested have ended in tiebreakers with the American leading 4-3 in tiebreaks won.

Karlovic, whose fastest serve is 153 miles per hour, set an ATP Tour record last month at the French Open when he struck 55 aces in one match.

“A lot of the points tomorrow will probably be like watching paint dry for the both of us,” said Roddick.

“Against Ivo there's so much that's out of your control. A guy serves huge from 6' 10”, a lot of times you're going to be walking side by side spectating.”

But despite his height and his monster serve, Karlovic has never advanced past the fourth round at Wimbledon, where the grasscourts greatly reward speed and power. Although at Wimbledon in 2003, Karlovic upset the defending champion Lleyton Hewitt of Australia in the first round.

Roddick has called Karlovic's serve “probably the biggest weapon in tennis.”

After winning this lone grand slam title at the U.S. Open in 2003, Roddick posted his best ever Wimbledon results in 2004 and 2005, losing to the world number two Roger Federer of Switzerland on both occasions.

Roddick or Karlovic could face the 6th seeded James Blake of the USA in the semifinals and the top seeded Andy Murray of England in the final.

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