WIMBLEDON, England ? The umpire lost track of the score. Venus Williams lost the match.

In a bizarre conclusion, the chair umpire called the wrong score in the second tiebreaker, and Williams fell in straight sets Thursday to Croatia’s Karolina Sprem in the second round at Wimbledon.

The Williams match overshadowed victories by Andy Roddick, Roger Federer, Lleyton Hewitt and Goran Ivanisevic and a second-round defeat for nine-time champion Martina Navratilova.

The 19-year-old Sprem, ranked No. 30, outplayed the second-seeded Williams on Centre Court, 7-6 (5), 7-6 (6), in the first major surprise of the championships.

Umpire Ted Watts incorrectly called the score as 2-2 in the second-set tiebreaker, giving Sprem a point when instead she should have been taking a second serve.

Both players appeared confused, but neither disputed the call. Tournament referee Alan Mills confirmed the umpire made a mistake but said the result would stand.

It’s the earliest defeat for Williams at a Grand Slam tournament since a first-round loss at the French Open in 2001. It’s also her earliest exit from Wimbledon since going out in the opening round in 1997.

Williams, who won Wimbledon in 2000 and 2001 and lost in the last two finals to her sister, Serena, didn’t blame the scoring error for her defeat. She had plenty of chances to force a third set, but blew three set points and lost the last five points.

“I don’t think one call makes a match,” she said.

Karolina Sprem returns a shot to Venus Williams. Sprem defeated Williams, 7-6 (5), 7-6 (6) Thursday at Wimbledon.

Mills said players had the responsibility to challenge the umpire if they felt the score was wrong.

“Unfortunately, the way it happened, Venus didn’t query it at the time,” he said. “They played point after point afterward and the result, I’m afraid, stands as is.”

The 47-year-old Navratilova, playing singles at Wimbledon for the first time in 10 years, lost 3-6, 6-3, 6-3 to Gisela Dulko — the same player who beat her in the first round of the French Open last month. Navratilova received a long ovation from the Court 3 crowd as she sat on her chair. She stood and waved to acknowledge the applause.