Stanford - Caster Semenya swept to victory in the 800m at the Prefontaine Classic on Sunday, extending a four-year reign of dominance that is under threat from new IAAF rules governing testosterone levels in female athletes.
The 28-year-old South African star, racing in her favourite event for the first time since May 3, cruised home in 1:55.70 at Stanford University's Cobb Track & Angell Field.
The two-time Olympic champion has not been beaten in the 800m since September 2015. Her winning streak includes 30 consecutive victories in major finals.
That streak was never in danger on Sunday as Semenya pulled away from the field with 300m to go before crossing the line 15 metres clear of second placed the United States' Ajee Wilson, who took second in 1:58.36. Raevyn Rogers was third in 1:58.65.
Before Sunday's Diamond League event in California, Semenya had not raced in the 800m since scorching to a world-leading 1:54.98 in Doha on May 3.
That outing came just days after she lost a court challenge against International Association of Athletics Federations (IAAF) rules forcing female athletes to regulate their testosterone levels.
The Swiss-based Court of Arbitration for Sport said while it feared the IAAF regulations were "discriminatory", the measures were "necessary, reasonable and proportionate" to preserve the integrity of female athletics.
Semenya successfully obtained an injunction against the introduction of the new IAAF rules on June 3 after a ruling by the Swiss Federal Tribunal, pending a full hearing.
Until a final decision from the Swiss tribunal, Semenya is free to run in the 800m.
If the court eventually upholds the earlier CAS ruling, Semenya will be forced to take medication to suppress her testosterone levels, or else switch to longer events.
In other events early Sunday, Rai Benjamin of the United States won the 400m hurdles with a world leading time of 47.16, taking the line ahead of Kyron McMaster of the British Virgin Islands (48.94) and Turkey's Yasmani Copello (49.37).
Benjamin's time was the ninth fastest of all-time and followed his victory in the Rome Diamond League meeting on June 6.
There was another world leading time in the women's steeplechase, where Kenya's world record holder Beatrice Chepkoech finished well clear of the chasing pack in 8:55.58.
Chepkoech's time was the fifth fastest in history. The 27-year-old now owns three of the five fastest times ever run over the distance.
In the women's 100m, Ivory Coast's Marie Jasee Ta Lou won a slow race in 11.02, with Americans Aleia Hobbs and Teahna Daniels placing second and third.