ATHENS, Greece - Andy Roddick hit one last errant shot into the net and hung his head, his medal hopes over.

In back-to-back stunners at the Olympic tennis tournament, Roddick was upset by No. 16 Fernando Gonzalez of Chile 6-4, 6-4, and defending gold medalist Venus Williams lost to Mary Pierce of France 6-4, 6-4. Both were third-round matches.

“I’m gutted right now,” said Roddick, broken once in each set by Gonzalez and distracted by a ruling that prompted a running dialogue with the chair umpire.

“It’s not every day we get to play this,” he added. “You can’t say, ‘Next year’.”

Late in his match, some spectators began chanting, “Chile! Chile!” When a group of Roddick’s fans responded with “U-S-A! U-S-A!”, they drew boos and whistles.

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The men’s final eight: Gonzalez vs. No. 8 Sebastien Grosjean of France, Taylor Dent vs. Tomas Berdych of the Czech Republic, Mardy Fish vs. Mikhail Youzhny of Russia, and No. 3 Carlos Moya of Spain vs. No. 10 Nicolas Massu of Chile.

Berdych, just 18, continued his amazing run, beating No. 15 Tommy Robredo of Spain 7-6 (2), 4-6, 8-6 a day after shocking No. 1 Roger Federer.

As a fitting nightcap, the top-seeded U.S. men’s doubles team of Bob and Mike Bryan were knocked off by Gonzalez and Nicolas Massu 7-5, 6-4.

So the men’s tournament is without its two biggest stars. It was a striking change of fortunes for players who met in the Wimbledon final last month, when Federer beat Roddick for a second straight title there.

Now Federer and Roddick need to regroup quickly before heading to New York for the U.S. Open, which starts Aug. 30 and is played on the same hard courts used for these Olympics. Roddick will be defending his only Grand Slam title there.

“Right now, I’m looking forward,” Roddick said. “I’ve got a pretty big tournament coming up.”

The hardest server in the world, he compiled 13 aces Wednesday but was broken once in each set, including at love to fall behind 5-4 in the second. By then, though, he appeared distracted by an extended argument with the chair umpire that began late in the first set and dragged into the second.

He found himself in trouble right away, broken in the third game. Roddick missed a forehand, then double-faulted twice, and Gonzalez smacked a backhand down the line to go up 2-1. Gonzalez raised a fist in Roddick’s direction and yelled “Vamos!”

Still, Roddick had an opening when Gonzalez served for the first set.

Unable to do much against the Chilean’s serve all match, Roddick was at 15-30 when he got a good read on a second serve and smacked a deep forehand return. It landed right at the baseline near Gonzalez’s feet.

Looking at the ball, Gonzalez paused, and the line judge called the shot out. Chair umpire Cedric Mourier of France quickly overruled, saying the point should be replayed.

Gonzalez questioned the overrule, putting his palms up as if to say, “Why did you do that?” Then Roddick chatted with the chair umpire.

They replayed the point, which Gonzalez won with a volley. On the next point, Roddick dumped a forehand return into the net and reared back to spike his racket on the court — but held on to it, as if he thought better. Roddick then dropped a forehand into the net, ending the set.

At the changeover, Roddick resumed his conversation with Mourier, making the case that Gonzalez’s body language persuaded the line judge to call Roddick’s return out.

“I could see it, clear as day,” Roddick said.

He kept talking while waiting at the baseline to start serving, then picked up the argument again during the next changeover.