updated 3:38 p.m. ET Aug. 29, 2004

ATHENS, Greece - As soon as the little-known Belarusian sprinter crossed the finish line to win the women’s 100 meters, the cross-examination began.

How did you improve your times so dramatically? What are your training methods?

Yuliya Nesterenko had never run under 11 seconds before the Olympics, but did it in all four rounds here — including a career best 10.93 in the final.

Minutes later, the line of reporters’ questions at her post-race news conference alluded to suspicions of drug use. Nesterenko patiently replied that her sudden success was simply came down to hard work. Then she passed her post-race drug test.

Such is the climate shadowing virtually every medalist’s performance in Athens — and not without some justification.

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A record 20 athletes have been thrown out of the Athens Games for doping violations so far, including Russian 400-meter runner Anton Galkin on Friday. More expulsions are likely over the final weekend: a Hungarian silver medalist in weightlifting was the latest to fail a test and come under suspicion.

Dozens more athletes were weeded out before the games even started; others stayed home for fear of being exposed.

The parade of disgraced competitors has left fans, journalists and fellow athletes wondering if they can believe what they see in Athens, especially in the wake of the BALCO steroid scandal in the United States.

But the atmosphere of doubt comes amid the most aggressive anti-doping effort in Olympic history. For decades, drug cheats were way ahead of the Olympic drug testers: Not anymore.

Olympic officials and doping experts say these games signal a watershed, brought on by a “zero tolerance” resolve within the International Olympic Committee, increased testing and targeting of suspected “dirty” athletes.

“In terms of drawing a line in the sand, we’ve done that here in Athens,” World Anti-Doping Agency chief Dick Pound said. “If we catch you, you’re gone. If we can’t catch you now, we’ll get you later and you’re gone.”

Already gone: 11 weightlifters, a Kenyan boxer, a Russian shot-putter, an Uzbeki shot-putter, a Belarusian high jumper, a Hungarian discus thrower and a Ukranian rower, among others. Two gold medals and two bronze medals have been stripped.

“Each positive test is a blessing for us because it’s eliminating the cheats and protecting the clean athletes,” IOC president Jacques Rogge said Friday. “The more we find, the better.”

When Greek sprint stars Kostas Kenteris and Katerina Thanou pulled out of the games following a scandal over missed drug tests and a suspicious motorcycle crash, IOC spokeswoman Giselle Davies held up their Olympic IDs for photographers and TV cameras like a trophy.

There were 11 doping cases in Sydney four years ago; the record was 12 in Los Angeles in 1984. There were five in Barcelona in 1992 and two in Atlanta in 1996.

“There is more aggressive testing and more aggressive enforcement than we’ve ever seen before,” said John Hoberman, an American author and doping expert. “There has been a sea change in the determination of anti-doping officials compared to the temporizing and negligent approach of the past.”

He attributed the shift to Rogge’s election as IOC president in 2001, succeeding Juan Antonio Samaranch, and the high-profile crackdown by Pound’s anti-doping agency.

Around 3,000 tests are being conducted in Athens, a 25 percent increase over Sydney.

None of the doping cases here has involved athletes from affluent, Western countries. Officials say the richer nations have more effective national anti-doping programs that catch athletes at home or act as deterrents.

The banned substances detected in Athens are drugs that go back decades, including stanozolol, the steroid that cost Canadian sprinter Ben Johnson his 100-meter gold in 1988.

“It seems to me people are using traditional anabolic steroids because they are still the most efficient doping substances,” IOC medical commission chairman Arne Ljungqvist said. “I think it’s a myth that there are many magic, undetectable substances around. THG was a special case.”

THG is the previously undetectable steroid at the heart of the BALCO case, which has led to criminal charges against four men for allegedly providing drugs to elite athletes. Five top track athletes have been suspended for THG use. Sprinter Marion Jones is under investigation in the BALCO case, but has not been charged and denies ever using banned drugs.

The IOC is testing for THG and the blood-boosting hormone EPO in Athens, and has indicated it may be screening for human growth hormone, or hGH, for the first time. Samples can be stored and tested later.

Meantime, the IOC is hunting down suspected cheaters, based on anonymous tip-offs and intelligence provided by doping control officials. But a side effect of their success is raised eyebrows every time someone runs faster, jumps farther or lifts more than expected.

Case in point: Greek 400-meter hurdler Fani Halkia broke the Olympic record in the semifinals and then won by a huge margin in Wednesday’s final, improving her time by nearly four seconds in the last year.

American hurdler Brenda Taylor, who finished seventh, was asked whether she was surprised at Halkia’s performances.

“Can I take the fifth on that question?” she said. “Yeah, she sure did come out of nowhere.”

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