The world sports tribunal has overturned a last-minute ban on long-jumper Darya Klishina taking part in the Rio Olympics.
Klishina, 25, was the only Russian accepted for the Olympic track and field but the International Association of Athletics Federations (IAAF) suspended her on Friday after new information on her doping record emerged.
After a day of hearings, the Court of Arbitration (CAS) announced that Klishina's appeal had succeeded and she "remained eligible to compete in the Olympic Games in Rio".
The decision came just in time for Klishina, a former European indoor champion, to resume her campaign for the women's long-jump competition which starts on Tuesday.
The appeal was the latest fallout from the inquiry by Canadian lawyer Richard McLaren for the World Anti-Doping Agency (WADA) which accused Russia of mass "state-sponsored" doping.
The CAS said it was Professor McLaren who provided the "new factual elements" about Klishina which led the IAAF to revoke her Rio eligibility.
The IAAF doping board rejected 67 athletes entered by Russia but accepted Klishina, who is based in Florida, because she lived abroad and had been through regular international doping checks after a cut-off period starting January 1, 2014.